Innkeeper.
I'm very surprised you were able to pay hotels in cash for amounts in excess of the limit, which is 1000 Euro. Hotels are usually more law-abiding seeing that they have to register guests.
Was this in last couple of years?

Apartment rental is another story and one in which landlords have a lot more margin for evasion as temporary rental contracts are rarely registered.
I myself rent an apartment for skiing vacation and pay cash, but my landlord always makes it clear that if he gets fined for tax evasion we share the fine.