Is it a standard practice in Europe to pay the bike mechanic minimum wage while charging >$100/hr for the service?
Can't speak for Europe -- but, generally, mechanics earn somewhere in the range of 1/2 the dlrs shop-rate. The pay schedules range from hourly wage, to salary, to commission, to commission plus percentage of parts sales (parts used in connection to shop work). Often negotiated -- a competent/agressive mechanic may want the last in that list, whilst a dealer may prefer the first.
There have been times when dlrs have advertised in trade journals for qualified mechanics and paid for the services of headhunters to find them so that their dealership can meet the requirements of the franchise.
Qualified shop mechanics proudly display certificates from trade schools and specific brand/model workshops they've completed/attended.
If you find a dealer that tends to avoid accepted practice, it's probably best to avoid them.