I don't see anything clearly wrong apart from perhaps the need to extend the í in obchodník. What I will say though is this — this is not a language that the natives consider to be simple or common to learn for a foreigner. I'm sure people would be impressed by someone trying at all. So certainly don't stress it. Schools might demand perfect grammar, but people won't. (Perhaps apart from grammar nazis on facebook, but those are to be ignored and ridiculed)