Sorry to hear you're having trouble with BestMark.
I have completed 2 shops with them and have a few more lined up.
They pay twice monthly so you can get a check quite quickly after completing a shop.
I got a report ater 1 shop saying there were some spelling/grammar/punctuation errors in my report. I found this strange as I always type my narratives in Word and check them before submitting. But I'm not going to get too upset about it.
They have very detailed instructions and some penalties if the shop is not completed accordingly.
But as with all mystery shopping companies, if you’re not happy with them you are not obliged to take any more assignments with them.