To be honest I don't think there is a difference, many companies sell products that say "as used by professional" or they call it "trade paint" to dupe gullible people into buying it!
Professionals just use the same as most other people but they are a little more wise as to what brand is best.
That is the difference - the amount of colour pigment present. Non-trade paints may also have additives to make them easier to apply for 'non-tradespeople'.