Just got my first bike rack, a trunk-mounted Bell Locking 3-Bike Rack. After a couple weekends of use I realized my rear bumper was scratched and/or paint scraped off in several areas... but it wasn't from the rack itself but actually from the inside-most bike on the rack! The inside pedal and front fork of the bike were actually scraping against the car as I drove. The design of the rack doesn't allow me to set the mounts further away from the car, they just slide down the bars towards the car.
I don't have enough experience with racks to determine if this is a problem with the rack itself, or if I'm mounting the bikes on the rack incorrectly. My car (Hyundai Elantra) does have a very small rear spoiler and the bottom foot of the rack is resting below the license plate instead of directly on it, but to my (untrained) eye it doesn't seem like that's the source of the problem.
Anyone who knows what I'm doing wrong or can suggest a jury-rigging that might work, I would appreciate it. I'm also wondering if some of the higher-end racks would prevent this from happening. The Saris Bones was out of my price range originally, but I might be able to swing it if I knew it would keep my bumper in one piece!