If you had something like Carsales.com (not cars sales as people don't search like that usually) then even with a hyphen you could do quite well, but it depends.
The search engines don't see any difference between having a hyphen and not, so if you can get it ranked well on the development you will still do well.
People don't generally go for them because of the word of mouth issues, but don't let it put you off if it is a great name anyway.
Rule of thumb to remember with most domains is to say it to yourself a few times, if it sounds like how people usually say it then it might have potential. Car sales is good, sales car is not.