Depends on how bad you flooded it. pull the dipstick and see what the oil level shows. if its above full then yes I would change oil. A little fuel in the oil will burn off, but a lot will cause lack of proper lubrication and could cause bearing damage not to mention if there is enough then chance of igniting those fumes in the crankcase. if the oil level is ok then hold the throttle completely open and try to start again. This will allow plenty of air in to dry out the intake and cylinders (just don't pump anymore). You may have to pull the plugs and let them dry out but its not necessary to replace them just cause they are wet from flooding.
Okay so I changed the oil and it started up beautifully for ten seconds but gasoline is coming out of the plunger nonstop. I just rebuilt the carb, so this doesnt make sense.
Did you set the float level? Or the float may be sticking? Give the carb a couple taps with a small hammer around the fuel bowl and see if it seats itself. Do you have a mechanical fuel pump or electric? Also could be too much fuel pressure forcing the float open. If so, you can regulate that pressure with an adjustable regulator (about 4 to 6 psi) is all you want.
You need to let him know. If you paid him then he needs to fix it. Try the tapping with a hammer first. Just a few light taps. If that doesn't work, call your mechanic.