I go by what I used to sell in the past, and start out by testing that particular company's scents. I used to buy a lot from Peak, but...well, not any more. SO, I buy the 1 oz testers, smell them, put one in wax...burn it..then if I like it, I'll go right back and get the lb size bottle if it's awesome. I'll also try MANY if the testers are on sale, gives me the opportunity to save a lot of money to at least smell them before buying a larger bottle.
We well a lot of fragrance oils (roll-on body oils), I currently have about 300 scents. The way I built up that supply was by picking a lot of standard scents, then by asking my customers what they wanted, and I'd order it for them by the very next week. If those ended up not being a popular scent, I'd drop it and choose another.
I also like to read these boards to see what the pros love