I handle these people the same way I handle the religious types that come around.

Step 1 - Yell loudly, "Just a second, I'm coming!" (can easily be misinterpreted)
Step 2 - Strip naked and toss on a towel and pair of cowboy boots, splash water on chest, hat optional
Step 3 - Throw cigar in mouth and grab bottle of jack
Step 4 - Open door and listen intently as they try to sell you whatever it is. Nod occasionally in agreement. As they're almost finished with a sentence, interupt, and invite them in for a drink. Tell them you'll take a bath with them and smoke cigars, talk about whatever it is they're selling.

They won't come back.