Having lived in France for 12 years and renovating (mostly) old houses, farms and barns, I've been into and seen hunderds of these. Some of them even containing a fortune in it. Like yours with old tools, but also with furniture, old cars etc.

A friend of mine made this kind of a business for himself. He made a deal with the former (or new) owners to empty the whole building for a certain price and with everything in it. Restored (or letting restore) all the usefull and good stuff and sold it with (sometimes big) profit to for ex. antique collecters or dealers.

Looking at these pics of yours brings back good memories.