In short, either you declare whatever it is worth to you with according insurance to hush your grief in case of loss. Either you declare as low value as possible and trust another fellow enthousiast. Sending as dirty (and kona stinky) as possible is also a good deterrant to TheAXe. You get way better deals on postage costs on meta sites (like parcelmonkey, postagesupermarket etc) that regroup several couriers as they have unbeatable deals with them. I recently bought an item on ebay and offered more than asking price but put the extra in form of postage costs to avoid extra fees. Guess what? Ebay put as much fees on the extra postage cost as they would have put on the item (we tried that option previously and thought we found a way around) ! No idea how ebay can justify that legally, to fully tax postage costs which were already taxed, but apparently it's ok for ebay to do it...
So the cheapest is buy in trust and keep everything low and send the rest as friend either in PP or other method. I regularly deal with people who trust nobody since platforms (especially since 2020) relentlessly tell you nobody is to be trusted ('only use our secure payment method') and that basically, before that, we all must have ripped off each other into oblivion... While they force you to couple your phone to your account (extra 'security' bs, been using the net and passwords since 1996 and never had one breach; yet big tech constantly proposes you to remember passwords, well if you need that you obviously shouldn't use anything requiring a password...), people have become increasingly afraid to mention their number. If a number was sufficient for those boogeyman hackers, they'd just type a number at chance no? If you don't want issues with accounts it simple: don't couple it to your number! As I'm an experienced seller/recycler, I usually quickly recognize scammers (a rare occasion but comes in waves) who do call by asking them a few questions. They have usual m.o.'s of only calling for expensive items. Let's say a car part that is compatible with many cars: you ask them what car they want to mount it on. Most scammers are so lazy (or it's not time efficient) they don't even read the ad description and so they can't even respond to what car they are going to use your expensive item for. There are many, many ways (with a bit of logic, not paranoia about the unknown) to spot scammers. If you're paranoid or lack logic, only buy new in the store and bring a knowledgeable friend. When you call, you can quickly judge who you are dealing with and even make friends (I do) and exchange valuable information without using electronic media. If you are a seller, remember you are nobody's slave and it's a sale on your terms. Not even sure if we should call it a sale with used items, as 99% of the time it is a partial compensation for the value depreciation (especially in real buying power of the date). So most times, it's a loss, not an income. It's a win for the environment and should be promoted instead of taxed.