Law / Selling a cello in Poland [4]

I'm in Germany and want to sell a cello as a private person. I've found an interested University in Poland that wants to buy my cello. Now, they say that for burocratic reasons, I'll have to sell my cello to a polish music shop, and they will buy it from them. All is well so far, but the shop now sent me a proposal for the sales contract. In this contract it is stated that the sale took place In poland, and that Polish law shall be applicable to this sale. I'm confused here as the sale in fact took place in Germany, where I live, and I don't know Polish law or speak Polish, so I can't check what I'm getting into. I feel that it should state that the sale took place in Germany, and that German law should apply. Am I being unreasonable? Are there any taxes or obligations I would have if I stated the sale took place in poland and Polish laws should apply?