ernie makes the customs himself.
haze is pretty much right except were noted.
i have found that the blade on customs is a little wider than the production strangely enough, only a little bit.
not all have zero bevel grinds though a lot do, some are CG and some of the older ones are "V" grinds.
sometimes the handle screws have a different pattern vs the production ie the '8 does i am sure. also as i'm sure ya know a lot of customs have ti bolsters which the std ones dont, also a lot of the customs have micarta handles but not all do, some ie the '8, have G10 handles. also a lot have chrome(polished?) handle screws and pivot screws though again not all do ie the '8 does not.
though the new ones have the thick liners a lot of older ones dont, i had an '8 which had IIRC the exact same liner thickness as a production '8.
i now have a '13 which is a little bit thicker in the handle vs the std '13.
several models are only available as custom ie CQC6 & viper.
productions bought from ernie run ~$550 or so, its when ya get them in the secondary market that the price goes up, up, & up, on most over $1K.
to sum it up a custom '13 and a production '13 are gonna be pretty close in the looks and size department, but not exactly the same.
they are very nice knives and imho are a good investment, for a knife anyway, they seem to alawys be going up in value especially the waved/bolstered ones, which are the hot ones at the moment.