Is it possible to fit a 36 hole rim to a 32 hole hub?
Theoretically? Yes. Practically? No.

the shopkeeper ordered a 36 hole rim instead of 32 one.

In most of the world this is his problem. You ordered new rim that will it your hub from him, so that's what you should get. Go to him, tell him you want what you ordered, that is a rim on your hub, or you want your money back and go to another repair shop  to make your wheel. If he opposes, then it is a question for sister site, Law Stack Exchange. But if you are in the European Union shopkeeper is on a losing position. I believe that's the case for most of the western world.