*tinfoil hat time* were I operating a casino and knew I had the only working implementation of my PRNG due to use of some clever tricks (ie mersene twister with diff primes and some binary shifts) I might try and take advantage of the occasional mark by forcing a loss and telling my verifier to report the numbers I choose for the player.
No obviously most sites have a verifier in javascript or they provide a script you can download to do the verification and players can do it themselves with ease.
Even better if its written in a popular scripting language and well documented (props to bitzino here).
But if you want to give players that warm fuzzy feeling you need to go above and beyond to reassure them, after all their confidence in your casino boosts your profits.
mem, good idea about casino operators giving offline verifier, this should be common practice as well that they should offer you to download all your bets in some file, they keep it all in their database, I don't get it why all of them give you access to just 50 lat bets, to me this looks like they are hiding something, all should be more transparent