Sale of photo

I was contacted by someone who wants to buy of photo of mine posted on flickr. I don't mind selling the photo but how do I protect myself? Are there scammers doing this sort of thing? (I actually think it's not a very good photo so I doubt I stand to lose by selling it).
Also this is a photo of a private house in Europe and the person wants to sell the photo for a commercial use. I don't have a release from the home-owner. Am I getting in over my head?
Thanks for responses.

No release no sale is my advise

Is it worth getting sue'd over $50?

I agree with goforphoto on this one.

Thanks guys, I'm taking your advice and bowing out. I learned a lot about releases from this forum.
Just a rank beginner.

I agree with goforphoto too, but can you get the release? If you have an idea of the location it may be worth it. Send along to the owner a nice framed 5x and the release form. If they say no then that's that, but let them keep the pic. But you never know you might make a new friend. I think that if you present a small gift and ask for permission you just may get what you need. Also make sure that the fellow that wants to license your image pays you well for the privilage.

Good Luck

Les Baldwin