I'll answer as a seller (of bags, but the same principle). Whatever price you put there, the buyers will try to bump it A LOT, even if it's super reasonable. The only bag I sold immediately at the original listing price was super-in-demand new Birkin, which hasn't happened since 2016.I’ve been clocking Cartier bracelets on there & some of the pricing is nuts. Why would I buy an used item for the same price — or more — than what I would pay in the store?
I am very clear that I'm going to loose money and sell new-ish bags with receipts at 50-60%, but people like to take the piss and offer 10-20%. The game then is to put high(ish) and see what offers come and adjust if there is no interest. Not saying it's always the case though.