5% Commision- You are being taken for a ride. Don't forget to add 22% VAT on top of that. You should expect to pay about 3%, but that is negotiable depending on a number of factors (primarily the value of the property). Considering how slow the market is now, you may have some leverage in negotiating.
Put on the Internet - You can always post on this forum and Gumtree in English, and place your own ad on Gratka & Domiporta.
JohnnyBoy:
selling it on quite soon
- That could be difficult in the current climate
Snag List - I'm not certain that snagging is too common in Poland. If you are going to sell the property, then you should leave it in developer's standard. In that case there should not be too much to snag. If you are going to fit out the interior, it will make it that much more difficult to sell. In any case 2000€ sounds very generous. How big is the property?
Good Luck