I recently sold a kids garden sprinkler mat, 4 months old and works fine but not quite what we wanted so we'll get something else. I advertised it and someone wanted it straight away so I fetched it in from the garden (we were getting one last use out of it so the last of the water would squidge out) and put it in a bag, but then she didn't show up. A couple of days later someone else said they wanted it and agreed to pay 1/3 of the retail price. The woman arrived an hour early and woke DS with the doorbell despite having a different time and being asked to knock, so I was a bit pissed off but anyway the upshot is that DH answered the door not me, so I didn't actually meet her.
She then messaged me to say "it's dirty". I know for sure that the top was clean because I folded it carefully to keep the top clean and explained to her that it was just a little mud on the base, that she could wash it off. I also advised her that as soon as she turns it on the water will make the base muddy from sitting on the grass, so she might not want to bother. She didn't reply but gave me a bad review on marketplace, which I haven't had before. While it would of course be nicer for her to get something clean and I would have rinsed it if the previous buyer hadn't been in a hurry, I don't see that it's such a terrible thing when it's secondhand and cheap. She also didn't ask to bring it back and she didn't say the mud didn't wash off (it's just thin streaks of mud), so is it really fair to leave me a bad review? I've only had positive reviews before, unless someone lets you down or the thing is broken it seems like a nasty thing to do.