Market maker prices do differ from DMA prices. Thats the problem. You basically accept whatever price the give you and they blame it on 'slippage'. Even when trading DMA at IG your stops are still OTC.
Ive had two examples recently where my stops were triggered and they filled me at a level(considerably below my stop) where there was minimal volume traded while there was massive volume traded at my stop price. Complaints were met with the "there will always be slippage" mantra.
