[WTS] Posting guidelines for physical goodsThis here is a good place to start, the biggest things are to show proof of ownership, and then focus on payments accepted and if your willing to use forum trusted escrow (that's the norm around here)
Those points surprisingly aren't your biggest issue with the listing, they normally are as many scammers try and skirt the issue to find a sucker. Looking at community standards on this board there is no "expectation" that the item has to be sold once listed, even if you say OBO, you can still turn down any offer. Just don't renege on a deal that you've agreed to. This changes if you say host an auction, I feel anyone starting these is making an implied contract to sell, if the minimums are met.
buckrogers laid things out really well, and followed up with a great response. Your running into a pricing issue. It's rare especially in this market to find anyone paying inflated costs, or give an honest second look at an overpriced add. Now again you are allowed to price your item how you see fit, but I would take the previous advice and really consider what you deem fair and reasonable and list there. You can pick a bottom line and say firm on price. The other option is using a different venue for your sale.
Good luck, and well done trying to learn how things are done here.