They say this is normal business practice in Poland.
They shouldnt lie, its not normal business parctice anywhere he should have just said i dont have a business bank account or im trying to avoid the tax man, or possibly you pay into my personal account and i dont have to pay vat and ill save you a few zloty in the process.
Checked out the site and they seem genuine enough, questions from me are:
1. do you trust them
2. do you have a receipt
3. have you been to their business address
If i remember rightly i paid a building contractor well over a 100 thousand zloty into a personal account but he was actually working on my house at the time.
You'll always have proof of transfer from your account anyway, if its just a web site youve visited i wouldnt want to pay. But then again you never really know the destination of PayPal accounts so its swings and round abouts really.