2: If I decide to rent out both the main house and this guest house within the calendar year that I perform this work, effectively converting the property to a rental property, can I deduct all this work as rental property upgrades?

You should be in and out of any flip in 3-4 months holding it for sale, that's not enough time for accrual to effect costs unless you're in the millions of dollars, in which case, your accounting department and CFO should be addressing the matter...LOL :)

This is also your first point at which some degree of error can be introduced, as AVM's are typically based on public record sales, and public records don't include attributes like view, curb appeal, and other less tangible items that can effect price.

@Thomas Morris I can't really advise you on this, but I know you want to make sure your decision is in compliance with the new Dodd-Frank rules that went into effect in January.

The speaker was VERY convincing, and managed to sign quite a large percentage of the attendees up to a 3-day real estate course for about $2,500; (I forget exactly how much as many discounts and what have you came into effect the more stuff you signed up for!)

I don't know MA law, but you may have to post notice to cure the condition before filing paperwork.If you terminate their lease effective July 1st and they stay, you'll have to start eviction then, and you'll lose at least a month.

Short of demo to the studs, is there any cost effective ways to eliminate the odor?

An LLC has to look like, operate like and effectively be a business.

They are not the ones that will be dealing with the effects of your decision.

It must be harder than usual to find motivated sellers as Power of Sale and banks selling for fair market value definitely have their effect on the market for motivated sellers.