So when the installer were installing your carpet, there was no furniture on it, right. It should be the same when we are stretching the carpet. However, due to the conditions, generally speaking we could get away with less furniture, but most of the smaller items should be off the floor.
Also depending on the wrinkles direction, some furniture might be in the way of the stretch job, so they have to be either removed or re-located inside the same room.
Home owner is responsible for the removal / relocating the furniture. But we could help you with limited amount, and could supply some sliders for the relocating the furniture.