Feel the need to introduce myself because although I've been a lurker for years, I just started posting recently. Any who, on my quest to find a great go to vendor...
I have bought from AE at least 8 times over the past 2 years. I was happy with 5/8 of my purchases. To find the vendors, I read reviews, looked at the # of orders for an item, always talked with the Vendor before placing an order to pin down details, and always paid through escrow (in order to be able to dispute). Pretty painless experience overall.
In addition, I bought a full lace unit from Holly about 1 week ago (my first purchase from a CV that was not from AE). I learned of Holly through BHM. We sent countless emails before hand so that I could make sure that I was sure. She was polite and extremely responsive. I even overpaid by 10$ (mix-up with the way I read the stock list) and she refunded it w/i minutes. I am happy thus far with my purchase. The wig was gorgeous.
Also, I purchased from countless AV's (genesisvirginhair, halleys curls, silkbasedclosures, etc) and I'd have to say it was about 60/40 split in my favor with regard to the outcome. I will note that with few exception, AV's offered considerably inferior customer service.
Oh, youtube reviews (from non-"gurus"... because I believe whether or not somebody pays for something skews their perception of its value whether consciously or unconsciously) are usually valuable in helping weed out vendors to stay away from.
In sum, countless hours on the computer and a really active paypal account is how I found good vendors.