All tours inside Auschwitz are run by museum authorized personnel only. The only value added from the tour company is the bus. The museum page warns of tour companies not making the reservation when you book, then canceling on you last minute, when they find there’s no space left. The museum states that tour companies have been doing this, and blaming the museum for being short of guides.
This is exactly what Krakow Booking just did to us. We picked their tour as they were listed in Rick Steves Poland guidebook.
I would recommend strongly that if you want to see Auschwitz you should make your own reservation. The only legit site is on the museum page. You cannot book an entry ticket within 5 days, and the tour company canceled on us just 2 days out. So unless you want to chance 2 hrs each way on public transport in the hopes of getting a last minute entry spot, book your own ticket. Don’t trust the tour company.