After a little sleuthing in the county records it looks like it's owned by an older couple who live about 40 miles away, he (I assume it's him) comes a couple of times a year with someone (not the same person twice) to help him wack down weeds in the yard and he occasionally takes a box of junk out of the house, while the back yard is full of old junk cars.

@John S Lewis  a few ideas, some easier than others...1) search lien records through the county2) check the system itself (panels and indoor hardware) for labels placed by the installer in case of service needs, pretty common, then call them up3) see if any neighbors have similar systems and ask them who they used, then call them up4) call local installers and ask whether they worked on that property5) looked up previous owners and ask them who installed, but check with installer about status rather than rely on the foreclosed party's representation6) Don't worry about it? 

My broker tells me if two parties agree contractually that the seller will hold onto and not record the deed on a seller-financed deal that, no, the buyer cannot later compel me to record the deed.

My broker tells me if two parties agree contractually that the seller will hold onto and not record the deed on a seller-financed deal that, no, the buyer cannot later compel me to record the deed.

My broker tells me if two parties agree contractually that the seller will hold onto and not record the deed on a seller-financed deal that, no, the buyer cannot later compel me to record the deed.

I THINK its in your best interest to file amended returns to record your depreciation and expenses. 

Wisconsin records are very open so most are already getting every single lead.

Also, I would not do some large change like add a bathroom or an addition that would change the particulars on the tax record. 

Don't forget to ensure you get all relevant records at close. 

If that amount is enough to pay you back with the interest, it may be worth you paying off his loan and doing a new, recorded loan on the property.If he is not getting a payoff amount to pay you off, you won't ever see the money.It may be better for you to buy the house for a fair price and rent it back to him.