Fuengi, as I understand it, you are an EA. (a.k.a. realtor, maakelar, whatever….).
If you don’t know how to find the m2 price, or at least come to some kind of judgement after reading Fotocasa and other websites that give it then I really do despair for your ‘profession’ in Spain.
Sorry if this sounds harsh. I’m just calling it as I see it.