Knock on the door of an Occupied Home pre-auction?

[Ian Turner]

Well, its that time of year when counties ALL across the country are gearing up for their tax sales.  BP has tons of great information on the ins and outs of sales but I didn't see this topic covered anywhere.  In conducting due diligence, has anyone actually take the chance of knocking on the door of an occupied residence that is slated to be sold?  

In my area there are a couple homes up for sale which I know are not occupied by the owner.  Occupants are either renters, friends, or extended family.  

Pros:  Better understand the situation, chance to view the property, chance to establish an early relationship with the current tenants, etc.

Cons:  Aggression?!, adversarial relationship (they may be planning to buy the home at the auction for minimum bid, now you come in and say you want to buy it too?).  Any other cons?

Any advice?  I'm talking about very inexpensive properties so even if something went sideways, the risks are pretty minimal considering the capital outlay they'll require.  Less risk is always better though!