That was part of the reason WF pulled the short sale, FNMA ordered and received the BPO and appraisal and WF didn't have it in their possession when the "Deadline Date" came.  

You never take possession of a rental property with bad tenants in it. your 'CYA" is to ask that it be 100% vacated and your do a property condition walkthrough X amount of days prior to close to make sure everything is as it was when the contract was signed.

In some jurisdictions you are able to demand "vacant possession" of a property or individual rental unit under certain conditions (i.e. you or an immediate family member are to inhabit the unit, the building is going to be demolished, the building/unit will undergo a substantial renovation which necessitates it being empty, etc).The answer to your second question will depend upon location.  

You might find the prior felony conviction for possession with intent to distribute (yeah, I found that), or the prior eviction (yeah, I found that too), or the recently repossessed vehicle (yeah, it sounds like a broken record - found that too).

The purchase addendum has some pretty strict language, especially about the previous mortgage insurance company can take possession of the title.

Normally  when I have gone to closing we do a walk thru, go to the closing table and sign, wire money or deliver a check,  and immediately get keys and take possession. 

If Tenant continues in possession of the Premises after the expiration of the Agreement Term, Tenant shall be deemed a holdover tenant and the tenancy shall be month-to-month.

Also, some title companies are beginning to refuse to insure title where the previous owner is still in possession.  

signed lease or no lease once you give possession of premises you must go thru eviction,

There are MANY hidden problems that are not seen by the average person and many do not come to light till after you take possession!