Read up on Steels
Knifesteelnerds.com is a great place to start with quantifiable tests, etc.
Try to go to shows and handle custom makers knives. This is a huge part of understanding what you like and don't. What fits your hand and what does not.
Looking at custom makers in a vacume is not as helpful.
Be willing to ask for feedback on designs.
If you like a makers work, and want to commission a piece, have the good sense to also listen to his feedback.
Don't go to a custom maker and ask them to make something they don't want to make, style, materials, size, etc, etc.
Some makers are so proficient they can make anything you want, to your specs, our if the materials of your choice. Often, they will refuse, because they don't like your design choices, sizes, stock material, etc, etc...
Try to buy, with a thought that you may want to later sell the piece, and go a different direction in your collection. This helps you in the long run. I can't tell you how many times I have seen people trying to move customs...Made to their specs.....andbe unable to move the piece...even at a huge loss.
I own a few customs. Often, I change direction, or want another piece from a different maker.
So far, I have not really lost money invested.
Less knives for more money was suggested above....I tend to think this way, some what....but have a bit of advice for buying from "budget makers"
I have a list of makers, who's fit and finish/ materials, skill, etc is greatly under priced!!
Don't discount a maker because his knives are priced lower than similar styles from other makers.
There are makers who will have super hot sales. Higher prices...and sell instantly.
There are makers with better finishing skills, higher degree of fit and finish, better grind lines, sheaths....etc, etc, who sell real bargains!!
That is something that is hard to relay, until you have held knives from both makers...and scratch your head.
Also, new/ up and coming makers can represent super values.
Carefully consider whether to sell a knife from a very hot maker, as replacement only gets more expensive if you can even get the maker to make you another!!