I had two weird experiences with @kansha who the other two traders (edit: a lot more suddenly since I wrote this) have great experiences with.
I bought an ER-301 which came with a component loose and rattling in the box, possibly broken off during transport but as likely to have been torn off when put into the snug bubble plastic bag. This was a year ago and after lots of back and forth, insisting everyone from the bag to the original seller, to the post office might have been to blame he settled on requesting insurance coverage from the post office. This was a year ago but no updates, no partial refunds ever materialised. I had to get the 301 soldered myself. I just assumed he was tired after the rather extensive dialogue related to that trade. Up unto the point the module turned out to be broke he was stellar but then he lost it.
Fast forward to today I jumped on a Three Sisters he was selling. He provided me with the wrong Paypal address (wrong domain, .de rather than .net which I sent for). I paid for that address while he pretty much at the same time sent a message correcting the Paypal which, well, I didn't register well enough (you'd think he'd be aware of his own email domain to begin with but apparently he needed me to more aware of the finer details of his correction for his incorrectly provided Paypal email). I did manage to cancel the payment but money locked down for 2-5 days, no big deal I guess but frustrating. I sent him an email saying something along the lines of "Wtf I sent it to the wrong address dude." which was enough for him to get combative while generously offering to hold the module for me (rather than the "ooooh sorry I messed up dude I'm sorry let's try again, forget about that Paypal fee I wanted to charge you and we'll work it out", or something)
If something goes really wrong expect to possibly end up in a worst of the internet styled argument, blame shifting, not pulling through on promises and no refunds or discounts.
Discussion thread about the trade:
https://www.muffwiggler.com/forum/viewtopic.php?t=200785