yes thats correct.
in fact its just one way the serious punters operate.
not sure if they are still there but in the commission rooms at the AJC some serious punters used to get a feed from the TAB showing the payout on each combination in the TRi.
they would then use an calculation of their own, combining prices and chances etc and " plug the gaps" in the market on trifectas and pick 4s

with W&P - you could just get the price from the screen and work it out yourself - as you know the problem is in a pari-mutuel scenario you don't know what everyone else is doing to affect the market etc so its still a bit hit and miss.