I, too, love pearls, and have a nice freshwater pearl collection.
Mikimoto is supposed to be the ultimate in pearls, but I've never had any of their items. On the other end of the scale, Honora (QVC) is affordable, and the one necklace I own seems nice enough.
I really don't think nowadays there are many pearl scams. Freshwater pearls have been greatly produced for about the last 20 years, and have gone down in price. What you really need to look for is the quality of the pearls--the nacre thickness and condition (nacre is the pearlescent surface you see on the pearl). If it's too thin, it can wear off easily, and is not as nice looking. If it's too thick, the pearl seems less lustrous. Check to see if any nacre is missing or flaking off.
Other tips:
1. Observe any blemished, such as "pimples" or bumps. A few tiny pimples are acceptable.
2. Are the pearls well-matched in both size and quality of appearance?
3. High-end pearls should be hand-knotted between each pearl. This prevents them rubbing together and is also a safe-guard against loss--only 1 pearl will fall of the strand it is broken.
4. Pearls come in many colors--some are obviously dyed (such as red pearls); most white pearls get bleached to improve their looks. Even white pearls have different tones. Try on pearls to see if you look better in stark white, champagne, pink, etc.
5. When being shown the pearl strand, roll the strand on the little pad they provide. Things should roll smoothly.
6. Pearls are measured in milimeters, mm. The smaller the mm, the smaller the pearl. Each increase in mm also rapidly increases the price.
7. If you are investing in an expensive necklace, and want it to wear it forever, consider only buying a strand where each pearl is about the same size. Graduated strands go in and out of style; matched strands are the classic style.
8. Don't pay attention to jewelry store grading systems for pearls. There is no such thing in gemology for pearls. For example, one store can say the pearls are "AAA"-quality. That's meaningless. (Other gems DO have legitimate grading systems, such as diamonds.) Use your own grading system--your eyes!