I don't buy/sell pinball machines, but I do buy/sell a lot of camera gear (for personal use, I like to try a lot of things and sell them along the way as I get bored). Firm price indeed coincides with at least a bit higher price than regular and also in my opinion indicates often a bit of an a$$h*le seller. Lowballers are far and between and most of them don't stop at "firm", they do it anyway on any ad they find interesting, it doesn't cost anything . I like ads without "price firm" and rarely if ever I answer ads with "firm" in them if the price isn't a little cheaper than average (and usually it is the most expensive among several active ads). It indicates a difficult person that knows his price is high but wants to rub it in your nose that he intends to stay at that unreasonable price without any space for flexibility. those ads stay for ever. I've had probably close to 100 transactions in that field and both as a seller or buyer 90% I hustled/got hustled for at least minimal correction of price. It shows readiness to interact with people and correct your perspective according to item condition and current market flow.