In most cases the reason they were not bid on, is they are undesirable and unsalable.

That will limit the amount of responses you get, thus filtering out some of the undesirable tenant situations, and garner you more rent. 

In this case you are not rejecting due to family status, which is protected, you are rejection due to a undesirable fit.

Not all tenants are clearly desirable or undesirable, so if a tenant is just so-so, or is a pain to deal with, and if he's been in place for a while and the property is in need of some cleaning and refurbishment anyway, the landlord might decide to end the lease and start fresh with a tenant paying higher rent.

Tenants come and go as do neighbors but you don't want to run the risk of making them not like you for bringing in people they may feel are undesirable. 

For the last three years I've owned multiple rental properties in an undesirable area in California with good cash flow.

I believe that a property doesn't rent, in most cases, for one of two reasons:1) The property itself (i.e. condition, location, other undesirable factors, etc)Or 2) It's priced too high.

A Group Home may be seen as an undesirable business/addition to the neighborhood to some of the local residents...

Regarding Dr Philips, are there undesirable areas?

Basically want to know the areas to absolutely avoid that are high crime and known for undesirable tenants.