I’d ignore any speculation about “signs” of a bad buyer. Great buyers also ask questions that can seem annoying before hand. Nervous buyers who ask for clarification can end up being some extra work but they can also be great, smooth buyers who just had a few questions.
All that really matters is knowing what your actual obligations are as a seller and what your actual risks are, so you can offer a fair resolution for both parties and, if needed, put your foot down in a way that is appropriate. Where some sellers get into trouble is when they have personal ideas of what’s fair or makes sense to them and those don’t align with the reality of what their obligations and risks are.
Shipping internationally complicates things* but, essentially, all you need to do is offer a return upon refund or a partial refund, as you have. If the buyer refuses both, your job is technically done, as far as obligations go. If they go to Discogs or PayPal, they’ll give the buyer the exact same options. There is no manner**
in which the buyer can use PayPal or Discogs to force a refund while keeping the record.
*If the buyer is, in deed, refusing to return, it could be because they know it’ll cost them a bit of money to ship back internationally. And they either don’t want to ask you to cover return shipping (or they have and you refused?).
**Sometimes PayPal will refund a buyer on their own dime and you keep the money and the buyer keeps the record. It’s rare but happens.
Now, as far as risk, you are not obligated to help the customer beyond offering those two resolutions BUT you run the risk of getting negative feedback and nasty messages. The former can hurt your shop and the latter can hurt your head/emotions, if you’re a softie like me who hates confrontation and getting angry emails. If the record is $25, it’s possible that it makes sense*** for you to fully refund them and let them keep the record in hopes they don’t leave a negative feedback comment. It’s not easy to quantify but having a lower seller rating and a feedback remark about how you were not easy to work with on an issue caused by your own packing could cost you more than $25 in future sales.
***For some people, the idea that a buyer “gets away” with being unreasonable is hard to swallow but IMO it’s not about them. It’s about what makes sense for you. Going back to the international return shipping note, it could cost you “$25 + original costly shipping + an extra costly return shipping fee + bad feedback + possible further damage to record on return voyage” to receive the item back and keep the buyer “honest”. You have to decide whether losing money and feedback is worth that. That’s a personal question that will have different answers for each person. For me, I’d save my own time and money and refund the person outright. I also don’t sell internationally because of the shipping costs, so I avoid the possibility of these scenarios altogether.