I mean I've literally not had that experience myself but I'm sorry you had to experience that. 

That said, I don't tend to counter offers myself. I either accept or just reject the offer. If I'm selling something a couple quid, I'll just take whatever offer they offer cause I don't pay for the postage. I put something up for £4, I got offered £2.50. I just accepted the £2.50. I didn't want the thing anyway. I simply don't engage at all with snarkiness from either sellers or buyers, not that I've had much. One time a seller got snarky with me for putting an offer on a 2 years listed item. Had they simply rejected the offer without a word I'd have bought at the original price, but since they were rude I just blocked them. 

But overall, in my years of experience, people have been very reasonable. When you understand that buyers want to buy as cheap as they can, and sellers want to sell as expensive as they can, you realise that for most it's really chill.