Some pigs will root and could potentially cause damage to flooring and doors.

I can't answer your legal question.But I have dealt with roots before.

Plumbers came out and found sewer pipes were clogged with tree roots.

Buyer did a specific sewer inspection and found corroded pipes with root intrusion under the concrete and the quote was $40K.

They have a product that is a new pipe relining system that will line the old cast iron sewer pipe lateral with a new, continuous pipe made out of resin to protect against future tree root infiltration.

It did just occur to me also, that I've also seen tree roots cause that kind of movement.

The current owner is open to selling it because he is deeply rooted in the town and knows the house’s history.

Many of those owner's don't wish to be long distance landlords and can't afford to sell.The perfect mentor might write you off in the first ten minutes of meeting you if you argue with them after asking for their advice, so be cautious of burning materials before you can even build a bridge with them.Everyone is rooting for you, go make it happen.

Although it is still in the beginning stages, competition is getting fierce and unless your already rooted in the market it would be tough accurately gage where its headed.  

The tree problem we've had in the south has been, after years of drought, the root systems have weakened and heavy winds in a storm topple more trees here now....even very healthy trees.