The central point we want to alert you to is that property agents in Poland regularly represent (and charge commission to) both the buyer and seller at the same time. However, it is also possible to engage the services of an agent who has no connection with the seller to negotiate on your behalf.
If you are sure you are going to have to pay some kind of agent commission (not necessarily true if buying a new development) then we would strongly suggest you engage a completely independent agent to represent you, unrelated to the agent included in the property advert.
This agent can still find you a suitable property (if you haven't already found one yourself) and make contact with the sellers agent on your behalf. The first advantage here is that they should more effectively represent you in the purchase process.
We would suggest that you also agree a fixed fee prior to viewing properties. If we assume that the headline commission cost would be zl. 15,000 +VAT (zl. 500,000 x 3%) we would begin by offering zl. 12,000 total, (including VAT). In addition to this, we would suggest that the translator, notary and property valuation fees are to be included in this commission.
What you are doing is incentivising the agent to find the ancillary services at the lowest price. This is something most of them can easily do but may not normally as they aren't materially affected directly.
This zl, 12,000 gross figure may be ambitious but as a starting point for negotiating the commission its as good as any. By forcing the agent to reveal the actual obtainable ancillary costs you can then focus on the cost of their services.
Be careful that you aren't too clever though and pay too little. If the agent feels they are not getting a good deal for themselves they may end up just getting in your way.