This is a long post but, without realizing it, I've been selling records casually for a long time and I feel like digging into that accidental well of experience for a moment. Lol.
It gets easier and less stressful to communicate with buyers who need help the more you do it. Very rarely is anyone 'pretending' to have an issue just to be annoying. Usually, they're telling you the truth and asking you to help them and an amicable, positive resolution is possible. IMO, it just takes a cool head on your end and a thoughtful choice of words when communicating to turn an "uh oh" customer into a happy one who will leave you positive feedback even when you make a mistake or the record gets warped/damaged in transit.
In the very rare occasion that a buyer gets unusually aggressive or seems like someone who wants to eat up your time, I've given myself the permission to cut my losses and lose some money in order to save sanity and time. I've been selling records (and other stuff) online since I was like 22 off and on, which is about 12 years, and I've definitely lost sleep over some buyers and transactions. In every case, I would much rather have had that time back to spend in a calmer, happier mood than those $30. IMO, it's setting yourself up for anguish, if you approach selling records the way a lot of users on Discogs and non-N&G message boards approach selling records. The customer isn't your opponent or adversary. Winning against potential 'scammers' isn't the goal. There are no 'tricks' to catch scammers or hacks to get PayPal to not enforce their own rules. In many cases, I incorrectly assumed a customer was upset or annoyed and, in hindsight, after everything went fine, I realized my read of the situation was off. Sometimes, I'm the one in a weird mood and I come off strong on a nice, well-meaning customer. IMO, it can be made pretty simple. You sell records. More often than not, you make a profit. Every so often, usually very rarely, you experience a loss. After that, it's your call whether to prolong your agony by fixating on the rare unfortunate transaction or whether you quietly move on and focus on the positive interactions (and profits) and the rest of your day outside of record selling.
Less philosophical and more practical advice is to troubleshoot your grading setup. Double check whether you are grading in a well lit area, whether your slip mat or platter hides warps (my Audio Technica table and slip mat really makes warps seem less pronounced than my U-Turn for some reason), and occasionally test records, if they've been in storage and unplayed for a few months. I've had records go from flat to warped over time, if they'd been on the shelf for a while between when I listed it and when it sold. Over time, I've gotten very good at knowing what light to use to spot dust/surface marks best, how to tell if a skip is permanent or a piece of debris that can be removed, how to assess warps, etc etc, but I'm certain I still make mistakes. I feel like even the best sellers with 100% feedback have made errors that deserve negative feedback but most people are nice and forgiving and don't leave negative reviews.
Anyway, I forgot what I was specifically talking about half-way through this novel.