From Diablo Wiki
Gold is the currency of all NPC merchant transactions in Diablo II, and is required to gamble, to purchase new items, to repair damaged equipment, and to obtain necessities such as potions, scrolls, and keys. Gold is readily available; monsters drop it constantly, it falls in showers from chests of all types, and loose piles of it can be found scattered about the ground in various dungeons.
While gold is required for NPC purchases, it's seldom used in the player to player economy. Gold is too common, too hard to carry in large quantities, and since none of the best items in the game can be purchased (a few extremely rare magical items aside, which cost more time than gold, in the form of endless NPC merchant visits) with it, players generally engage in a barter-based economy, trading items for items, or else using small items such as Stones of Jordan, perfect gems, or runes for a sort of default currency that replaces or supplements straight item to item bartering.
 Gold Acquisition
The easiest way to obtain gold is to pick it up when its dropped by monsters or chests. Gold picked up in multiplayer games shares evenly between all party members on that level. If there are 5 players in a party, but one of them is in town, and one character picks up 1000 gold, he and the other 3 on that level will instantly gain 250 gold.
Gold is not shared between players who are not in a friendly party, (this feature can not be disallowed) and it's not shared to players in the party who are not in the same area. In this usage, area = level, and the level is all that matters, not proximity. Two characters half a screen away from each other, but in different levels, will not share gold (or experience gain), while two characters ten screens apart, but in the same level, will.
If one or more characters in a party are at their maximum gold capacity, the gold picked up will be shared amongst those who are not yet full. This can create an interesting situation if a character who is full of gold picks up a stack. The amount to share will be deducted from the stack, and the rest will fall back to the ground. A character can therefore click the same stack several times and watch it steadily shrink down to nothing, reducing by halves or more, depending on how many other characters are in the party.
 Gold from Item Sales
Besides picking up gold, most characters make substantial profits by selling items to merchants. The maximum amount merchants will pay for any item is set by Act during Normal Difficulty, and then increases another 5000 on Nightmare and Hell difficulty, in any act.
- Normal Difficulty:
- Nightmare Difficulty: 30,000
- Hell Difficulty: 35,000
The most expensive items to sell are pieces of body armor, helms, and magical weapons with +spell charges, such as wands, scepters, orbs, and claws. The most profitable items, by inventory space, are generally wands, which often go for 35,000 and require just two inventory spaces. Virtually all exceptional and elite body armor will sell for 35,000, but they all require six inventory spaces. Weapons are much more variable in value, depending entirely on the modifiers they spawn with. Set and Unique items are priced by fiat, with their sales values preset in the game code, and they are generally worth far less gold than magical or rare items with similar modifiers.
Gems are often ignored, but they are quite valuable, especially once a character is on Hell difficulty where the gems dropped are usually flawless quality. These sell for 7500 each (skulls are double the price), and thus 6 flawless gems are worth 45,000, compared to a piece of body armor that will sell for 35,000 at most. The value of gems is boosted by the fact that they only take up 1 space in inventory, and will fill in empty inventory gaps around larger items.
 Increased Gold Find
Items with the "increases gold find" modifier increase the amount of gold dropped by monsters and chests by percentage. These items do not affect merchant prices (though some unique items will lower the prices charged by merchants) or change the mechanics of party gold sharing; they simply increase the total gold dropped. These increases can be quite substantial; it's not difficult to assemble equipment with more than 500% increased gold find -- over 1000% is quite possible -- and characters who wear such equipment and take the time to pick up levels full of 2000-3000 gold stacks almost invariably have better gear than most characters, thanks to all the incremental equipment improvements their constant gambling creates.
Increased gold equipment creates wealth through a sort of psychological trick. Characters without any gold find tend not to pick up any gold once they're past the early levels of poverty, since the 200-300 stacks don't seem worth the trouble. In contrast, characters with good gold find tend to pick up most of the gold they see, since it drops in stacks of 1000 or more, an amount that motivates the collection. As a result characters with gold find don't simply make 400% or 600% more gold than others; they make far more than that, since they're picking up big stacks of gold while others aren't picking up anything at all.
This equation changes for characters who are heavily twinked out with high quality gear, or in multiplayer games with gold sharing, but it can be very interesting to play several single player characters, focusing some of them on gold find, before comparing their equipment at level 50, or 70, or 80.
 Gold Loss
Characters drop a percentage of their gold when they die. The formula for the gold dropped differs slightly between multiplayer and singleplayer characters, since SP characters will never lose all their gold. (These same rules apply to hardcore characters, but in their case gold loss is the least of their worries.)
Multiplayer characters drop a % of their total gold (character + stash). This amount is equal to their clvl, capped at 20%. For instance, a level 50 Paladin who had 100k on him and 900k in his stash would drop 200k gold upon death. This is the "death penalty" that strikes no matter where their gold is held.
After that amount is calculated, the character drops all the gold they were carrying before the death penalty was inflicted; this gold may come from the stash if the math requires it. Returning to the level 50 Paladin mentioned above, he would drop 200k for the death penalty + another 100k since that's how much he had on him. Of this total 300k, 100k would necessarily be taken from his stash, since the total exceeds the amount he was carrying. If he'd been holding 500k and had 500k in his stash, he would have dropped 20% of the same 1,000,000 total, and then dropped another 500k, bringing his total loss to 700,000. This explains why it's prudent to sock gold away in the stash when you visit town.
Single player characters differ from this slightly, in that dying will never leave them broke. They do not lose gold from their stash when they die, and 500 gold per clvl is exempt from the death penalty. If a level 20 single player paladin died with 10,000 gold to his name, he would not drop anything. (Just self respect.)
 Carrying Capacity
Characters can carry more gold as they level up, and this increases at a constant rate of 10,000 per level. A brand new level 1 character can hold up to 10,000 gold, a level 15 character can hold up to 150,000, and so forth, up to 990,000 on a maximum level 99 character.
Gold does not require any inventory space in Diablo II, nor does the weight of it factor into character movement speed or stamina drain. Gold should be regularly placed in the stash, which has more capacity than a character. When used for purchases from NPCs, gold is first taken from a character's pocket, then automatically deducted from the amount in the stash, if necessary.
 Maximum Gold Capacity
The most gold a character can possess (not counting stacks left on the ground, which will decay and vanish after 10 or 15 minutes, assuming other players don't steal them first) is 3,490,000, at level 99. That's 990,000 on the character + 2,500,000 in the stash.
 Stash Gold Capacity
The stash's gold holding capacity also increases with a character's level, at a fairly even rate, with one large exception. After allowing less than 200,000 through most of normal difficulty, the stash rockets up from 200,000 to 800,000 at level 31, then goes into a slow but steady climb, gaining 50,000 in capacity every two character levels until it maxes out at 2,500,000 at level 98. See the full table below.