Some people chuck a fancy name on an unknown coral and charge through the roof and make hundreds off a $50 piece.
There's nothing worse than seeing "super master multicolour skittle rainbow burst acro!" Being sold for $200, buying it, then in 6 months realising it's a fairly common, fast growing coral you can't get rid of for $50 because everyone else already has one or five at home.
Those of us with more than money on the mind will just sell them for the average going price for a non-fancy-shmancy-named frag. Colour, pattern, growth rate and hardiness are all major factors of price. If you have a super fast growing acro with drab and dull colour, it won't go for as much as a super bright multicolour frag that grows slowly.
If you're asking because you're looking to sell some frags, have a look at similar species with similar colours and make your best judgement call based off that. Worst case scenario, you drop the piece a little before selling.