I have came to a decision..
You will not pay from quoted price again, you will pay from final price, if the worker quotes 10M and you sell the service for 15M, you will pay the worker from the 15M not the 10M they quoted. Your t.o.s doesn't state 10% from quoted price, it says 10%, which implies 10% of the order.
I have talked to a sythe global mod which confirmed they think you are scamming, so I'm assuming if this happens again you will be ip banned from there also.
Negative feedback will stay, you have been doing this for a long time and yes you say its never over 5M+, but you do realize if you've done 100 orders(which you've done probably 300+) and charged an extra 1-3M each time or even half the time, you are basically scamming the worker out of 100's of Mills.
Next time you will be ip banned if you get caught doing this again.