I've ordered alot of hair both from Dollyhair and Mylittlecustoms. I've personally never had any problems with Dollyhair. Only once was my order delayed, and they sent me another package of hair for free as an apology.
The main reason I buy from Dollyhair over other places though: Dollyhair simply seems to send more hair and its also cheaper. With Dollyhair's bag of hair you can easily rehair 2 adult ponies, but with Mylittlecustom's bag of hair I was able to hardly rehair just one adult pony. And the price being $3.12 vs £3.50.. Well yeah. I hope I will never have problems with Dollyhair.