One tool is to look at historical data and determine prior market highs as an historical indicator of what prices in a given community have reached in order to make a determination of likely price returns to those levels.

The former owners may have moved back in prior to the actual foreclosure auction, which could have been rescheduled many times.  

I plan to do one next year (refinanced out of my prior FHA on 4plex) for another 4plex that better suits my needs and neighborhood choice now.

If you discover the repairs and removal are excessive you can communicate your concerns to the seller in the form of a new offer at a lower price OR request that they remove the tank prior to closing. 

this would give the compressor a direct link from the garage to the house. some electric motors ( which this compressor has) can force a back feed as though it were a generator. this would cause the compressor to back feed directly into the main panel and overload the whole house without passing thru the main breaker in the main panel. we could have a twofold problem here. a defective compressor and a direct ( wrong wired) connection. in any case, this tenant had no business messing with the electrical system of your house and could have cost you the house and perhaps some lives. this would be grounds for me to evict or not renew the lease. if there were no problems prior to this, the loss of his tv sets are his fault not yours. throw the bum out and for safety sake, have another electrician check things out completely

I would probably chat with any lenders that you have a prior relationship with.

It sold within six months and the leaser, prior owner of the property, signed a 5 year lease for monthly rent for more than the buyer could get from another tenant.  

Does anyone know of any other ways that we could mitigate or eliminate the risk of them not leaving prior to the October 31 deadline?  

100% agree with the prior posters to run away if those HOA and taxes are the annual figures.

I'd think you're starting off on the wrong foot thinking along these lines unless there is a agreement and significant assets in play that others may be entitled to, such as children prior to the marriage.