It's easy but takes practice and while videos give you a good idea being taught by someone is better it give you a better idea the pressure that needs to be applied.
If the herp vet is really a herp vet n someone that just tell you that yes they will see your reptile they should be able to sex it for you.
Personally rather than pay for a useless vet visit I would rather find someone local that has experience because it not a bad thing to learn.