TMAM. there is another “trick”, for lack of a better word, that some dealers employ and is called a “cost code” or whatever.
It is a combination of 10 letters, numbers and/or symbols that you determine for yourself that represents the numbers 0 thru 9 ….. and then when you purchase an item you put a “tag” on it with the price you want to sell it for ….. and what you actually paid for it via your “cost code”.
Anyway, 40+-% of your patrons will pay you the listed price and 60+-% of your patrons will either “make an offer” or ask ”how much will you take for it”. Thus, via your “cost code” you can quickly determine how much you can reduce the price without losing money.
Some dealers also put a “date of purchase” on their more expensive items. The reason for that is, you don’t want an expensive item sitting around your store for 6 or 10 years …. because that will cost you money. After so long, …. sell it, … for whatever you can get out of it and put that money in a new item(s) that can be sold for a profit.
Cheers