I did knock someone's house to see a model which is under the same builder but in different neighbourhood. There was only one house with that model in my neighbourhood, and it happened the owner wasn't home. There were 3 people in the waiting list to the lot I held at that time. The builder couldn't help me. But she gave me a suggestion to see the model in another place. She told us it would depend on my luck if the owner could show me or not. It was lucky to me, the owner let my family in, and he gave us a lot advises about the builder. But this house has a big irregular size. The structure of the house has been changed from the model. I was very appreciated about that. I am thinking he could let us in, probably because we carried an infant, and didn't look like bad guys. We decided to take the model. When we were in the sales office to sign the contract, suddenly my husband asked to give us 15 minutes to try to see if someone was in the house which has the same model in my neighbourhood. Because the same model house could be slightly different applying to different sizes of lot. When we knocked the door, there was an old lady who opened the door, and let us in after we explained. She told me she was the tenant. She was quite happy to show us the house. This time we find out the size of the kitchen was small comparing the size of the house. We went back to the sale office, and decided to take another model. We were so happy we had chance to see the model at the last moment.
So I did two times knocked two different houses. Both were accepted. By the way, both of them were not Chinese. For sure the owner has the right to show the house to other people or not. But it might help others a lot if you do. On the other hand it is your judgement to prevent others might have other purposes.