In such informal sales, isn't it customary to make lower offers? I don't see that the reason given for the sale will have much impact on this.
I assumed you were selling your items online, in which case I would expect you to specify a price. If it's a fixed price sale, then the buyer can't make a lower offer. If you sell it using an auction system (like eBay), then you specify a starting (minimum) price and hope that people will want it badly enough to offer a higher price. Either way, if I saw an ad for something and there was no price on it, I would ignore it and move on to something that was priced.