"...strike a deal ...faster than you can blink." That may/could be the wave of the future. Still, as regards to that happening in Germany, I won't hold my breath. In the last ten years of staying at various small hotels, Pensionen in Germany, (Berlin,. Münster/Westf., Frankfurt, Munich, Minden, Düsseldorf, Hamburg, Sigmaringen) aside from German chains, none of them was run by grandma types, all run by people then in their 40s and 50s. Maybe grandma runs " Zimmer frei" arrangements, (I don't know). That option I used only once.
In Berlin the Pension I used to stay at (down from Savignyplatz) before the Russians got it in 2006, stayed the same with the new Russian owners with a few modifications made, eg, installing a shower in the single (EZ) where there had been neither toilet nor shower. Still, the newly refurbished room had no toilet. You reserve the same old way, they prefer being paid in cash, (don't think they accept a credit card), no AC nor elevator,
The Pension that I use now since 2009, be it 4 nights or 14 plus nights is run by a mother/daughter team, not listed on booking.com, mother is non English speaking, no elevator, no AC, no phone in the room, only last year was English news programming with CNN introduced, some rooms come en suite. others only with a wash basin ("mit fließendem Wasser") Of course, with such characteristics you are not going to see very many international tourists, especially anglophones...very true based on my own observations and looking at the guest book. You can be certain that such establishments still exist in Germany, and not only to be found in some town in the sticks, be it in Hessen or Bavaria, or Mecklenburg and Schleswig-Holstein if Berlin is any example.