There are courses available to learn how to tune.
Hoever they are not cheap. Add to that the fact you then need to hire (@ 150 odd dollars an hour) or buy (@ 150k plus) a dyno, and suddenly you realise you may as well pay an expert to do it. If you want to give it a crack though, buy a lambada, and dont try it totally off the bat.... a motor isnt worth it
And whats been said above - shops will always big note thier own work before others. And everyone tunes with a slightly different philosophy.
End of the day if your happy with the tune and it doesnt pop your motor, be happy. Every person will give you a different reply on the standard of work from shop a b c and d, you need to go in , ask questions, make a judged decision, and hope its the right one.