They accepted that at signing and that was that until I decided to replace it and added an addendum to the lease stating that it was functional.In the future, check all working items in your property and make sure each non-function item is listed.

Can your contact provide you with any performance details of other tiny houses in the area?  

Go over terms on the sale you both want to see on a scratch piece of paper .. then give that to your lawyer ..Your lawyer should draft up an agreement and send it to his sellers lawyer . they hash out the fine details and come up with a sellers agreement everyone can live with .everyone signs that at closing  Atleast that’s how mine have went 

So I do tell the buyer all details about the property.

Install an extra kitchen, bathroom, bedroom, exterior entry door, and all the items needed for another unit.

Just be careful the new agent isn't "tickling your ears" just to win your business.Be sure to fill us in on the details once you're finished. congrats!

Also, I would like to get a real estate attorney to go over it and explain it in through detail.

Not to get into too much detail, I had a transaction earlier this year where I represented the buy side, and that seller at the closing table had to write my buyer a check for $15k for not disclosing something that state law required them to. 

@Andrew Schaefer  Thanks again for the detailed response, awesome feedback. 

I'm not at all familiar with PA, so I can't give you any details.