I've told them that I would give them at least 48 hours notice, and they've told me that they'll sue if I don't pay them $50 each time I show the house, because they are worried that I will show the house to a registered sex offender.

You do a search and find that a registered sex offender occupies one of the units. 

He was told that the landlord would be coming over and bringing potential renters.Depending on where the property is, the tenant is looking at anything from a cop telling him to knock it off, up to prison time and registering on the sex offenders list for life. 

His solution was to rent to the very group that have the greatest difficulty finding access to housing: registered sex offenders.Ok.

Saying a pre-nup sets the precedent that you expect the marriage to fail is like saying giving condoms to kids encourages them to have sex.

Or should an investor opt for same-sex residents?

It is legal to collect advance payments here but maybe they have a problem you have not discovered yet like being a registered sex offender or something and want to lock up a long term before it is discovered.

Information on the tenants Look up the crime rate in that area Look up nearby sex offenders that are registered - it can be good to know how many and how far away they are in case you rent to a family, etc.

Covenants, conditions, and restrictions (but omitting any racial restrictions indicating any preferences, limitation or discrimination based on race, color, religion, sex, handicap, familial status or national origin), if any, appearing among the public land records.

This time to talk to me about how he was sorry and that if I would sign a document stating that I never had sex with his ex, he would like to do business with me.