When your trim settings are correct, after you let off the steering it should continue straight in the direction it was going when you let go of the steering wheel on the pistol transmitter. Mine is weird, If I last turned to the left it will SLIGHTLY pull to the right and I can trim it back to the left to get it straight, but by doing this, next time I turn to the right it will slightly pull to the left after I let off of the transmitter. I've dealt with rc's for 15 years, I know about the servo reversing and trim adjustments something is wrong, I don't know if it's the servos or cheap radios and receivers.
I have tried several different radios that are all doing this, but I haven't tried changing all of the servo's yet, I just can't believe that all of my rc's would have bad steering servos
Let me add that it isn't just one rc car doing this either, I have noticed it on 2 or 3. I have about 15.