Years ago when paying with PayPal, there were 2 choices - for them to convert currencies or to rely on my bank to convert them. There was a warning that if I chose the second option, it could cost a lot. Turns out, with my bank the conversion was good and with PayPal's conversion I'd lose like 10%.

Stuff like that is what I say "years ago" - I haven't used PayPal for a while now, and I won't use it again.