muckles:
Services and motorway parking in much of Germany fill up fast much like many other places round Europe. I often have better luck with the Autohofs, especially as many now charge for parking, which is refunded in full if you buy a meal, but does put off those who don’t want to buy a meal or whose bosses don’t pay parking.
Did manage to park at one that didn’t charge at 2am on a trip back from Frankfurt last year, although that was in the car parking area, but nobody seemed to mind.
Most bosses don‘t pay for parking.
If you park on an Autohof and pay something like 15€ than you put it against your tax. Also a meal voucher will be inculded, like you said.
You can put recipts for toilets and showers against tax too.