Paypal takes 2.9% + $0.30 on each transaction unless it's actually refunding a previous transaction. In the case of the refund, the transaction fee is also refunded. However, most people are fucking idiots and don't realize this, so they just send it as a normal transaction and get dinged twice, essentially giving Paypal 5.8% + $0.60. Anything above this that the artist withholds and claimed as "paypal tax" is a flat-out lie. I have been using Paypal regularly for 18 years.

i think it only does those transactions when its like across different countries

for me this happens alot from paying GBP pounds into USD dollars

If the artist repaid you in full despite the fact that you got some work out of it, you're lucky you got a full refund. Most artists will refund you for the work they haven't done, because they've still put time and effort into producing some work for you and that's time they're not getting back. If you've got that work, they have a right to a portion of that money.