My husband was sitting on the couch and working (and fortunately he decided today was a good day to wear pants instead of pjs) when our front door was unlocked and a woman walked in, with a prospective behind her. 

HUD nitpicked a bunch of stuff, including having to put a lock on a door that all tenants needed to use, and was normally unlocked, which was really inconvenient for the tenants (forget the details, but it created a hardship for them all). 

In some situations, I can understand why the landlord would chance it than follow the exact letter of the law.Of course, if my best advice isn't followed I do recommend that the landlord take detailed photographs / videos of any property that was left behind.

I have 2 master keys, a Kwikset and a Schlage that unlock everything I own and will unlock everything I ever buy.

(I have the photographs of the signs posted on the property for the upcoming sales and I have the Patriot News paper copy that shows they posted the Upset sale in the paper)Q?

It happens so infrequently for us and we live within 10 minutes of all of our properties, so we just go and unlock the door for them.

even without unlocking the door someone can break the glass and climb through the window of the door. 

Your opportunity as the investor will be to run the building better and unlock additional value.Here are some strategies I use to maximize revenue and expose turn-over opportunities.- Begin raising the rent like clockwork on the 1st of the year- Look for violations in the existing lease including pets, people, etc.

Any carpet cleaning company should have UV lighting systems that will show urine staid for photographic evidence.  

As soon as you see damage, photograph it, and give her notice that she must vacate or whatever your first step to evict for damaging a property (breaching lease?)