Simple Auction Mechanics

In a recent session, I had an auction of magic items and other artifacts and wanted to share the simple mechanics that I used. The goal was to have a more random and interesting way to acquire items.

The setup:

1. Make a list of 3-5 items for bid. Most should be randomly generated to model the feel of a random auction. For added intrigue, you can reveal only some info about an item (for example, a "magic ring" could be up for auction but they don't know what it does).
2. Decide on a starting bid for each item, perhaps 60-70% of what a shopkeeper would charge.
3. Decide on a bid increment for each item. If the starting bid is 150 gp, a good bid increment is 10 gp. (This doesn't have to be exactly balanced. Prefer easily countable increments.)
4. Decide how many other "bidders" are interested in the item to start. A useful magic item may attract 10 bidders, while something less popular may only have 5 or 6.

The auction:

1. Start by allowing the party to bid the starting amount if they are interested in the item.
2. Roll a d20 for each NPC bidder. If the result is a 10 or higher, that NPC is willing make the next bid. Remove any dice that are 9 or lower. If no NPC rolls a 10 or above, the PCs win the auction.
3. If there are still NPC bidders, allow the party to bid higher if they are still interested. If they decline, an NPC wins the lot.
4. Repeat steps 2-3 until a winner has been decided.

Example:

Item: Winged Boots

Starting bid: 100 gp

Bid increment: 10 gp

Bidders: 7

1. Party makes a starting bid of 100 gp.
2. NPCs roll: 18, 13, 14, 4, 5, 18, 7. Four bidders are still interested and bid 110 gp.
3. Party bids 120 gp.
4. NPCs roll: 16, 4, 7, 12. Two bidders are still interested and bid 130 gp.
5. Party bids 140 gp.
6. NPCs roll: 4, 9. No bidders are interested, party wins item for 140 gp.

Have you ever used an auction in your game? Let me know what mechanics worked well.