If you are getting numbers changed on you a lot then probably you are falling into a pattern in your betting. The only pattern I could see is betting a lot of dogs since they mark up the chalk so much, but then again if they are truly getting mostly chalk players they should be glad to give you some action on the dog. Double dealing lines isn't that bad a thing to a bettor that shops around and any smart manager can see that they will end up losing far more action than they desire to lose if they take it too far. If you always got a worse line on your sides, you probably take your action elsewhere. In games where a book is badly sided they may not mind, but if they accomplish nothing but chasing off action then the book is just being stupid.
