What are the ways to look inside homes for sale without anyone?

[Tom Smith]

What are the ways to look inside homes for sale without anyone? I know there are Open Houses and New Home sales offices, but can I go into these homes and look around myself without any one being there to sell me something? I have never been to an open house so are they usually trying to sell you something or do they let you look around as you like and not bother you? Are there any other ways to check out the inside of a lot of houses for sale without anyone being there?