...that the buyers who are most likely to email you to have a moan about something are the ones who got a complete bargain and bought something really nice for tuppence ha'penny.
Honestly, there have been times when I've sold something for more than I thought it was worth, even though I'd described the item accurately, and I've been wibbling that the buyer was going to be disappointed with the item and leave bad feedback. But those sales always seem to end with the buyer leaving happy positive feedback stating how much they like the item even though they've just paid £12 for a knackered old Mini-Boden fleece or £60 for a faulty Dualit toaster, or whatever.
OTOH:
When something that I think is quite nice goes for 99p or £1.20 or whatever, quite often the buyer, instead of being pleased that they got a fab bargain, will email to complain about something minor, or completely beyond my control, eg. that I used recycled packaging (er, yes, good for the environment, dur), or the item doesn't fit (despite me putting all the actual measurements in the listing) or the colour is not quite what they were expecting (despite all my lovely well-lit photos), or whatever.
Meh. This buyer wants a postage refund because I used recycled packaging (yes, like it says in the small print of the listing, read it, why don't you?) and she reckons the item went as a large letter (no it DID NOT, I sent it as a small packet, it will def have been too big to fit through the large letter slot). I use a postshop, and I think their postal stamps don't have the actual price on the item, so she can't actually see how much the postage was, she's just trying it on. Grrr. I have refunded her £1 as a goodwill gesture, otherwise I know she'll leave arsey feedback. But really. It's always the ones who've got a great deal who are dissatisfied.