Susan,
Finding a good rep. is like finding a good plumber or car repair shop (well, maybe a little more complicated) but can basically be accomplished by internet searches or through referrals from industry contacts you have. A good rep. has experience (preferably within your industry or relationships with retailers you are trying to get product placement with), is responsive, and has a good reputation in the industry (usually you can ask for referrals from their existing/past clients). I hope this helps.
Thanks,
Traci Cook