Puncture repairs are limited to the center of the tread area. If there are punctures or damage in the shoulder or sidewall of the tire, it is not repairable. Guidelines allow the repair of punctures in a tire's tread area of up to 1/4" in diameter.
Any repair attempted without removing the tire from the wheel is improper! Without inspecting the inside of the tire for hidden damage, there comes the risk of returning with a weakened tire to service. In some instances, punctures in the tread area that looked repairable revealed upon further investigation the object that punctured the tire had been long enough to cut the tire's sidewall from the inside. Without dismounting the tire, the hidden damage would have been missed.
Beware if they say they can repair a tire in 10 minutes for under $10 dollars without removing it from the wheel! they aren't following the Rubber Manufacturer's Association procedures! A correctly done flat repair that follows the multi-step repair procedures will take approximately 30 minutes and probably cost around $20-$30 or more.
A flat or mushroom-shaped patch and plug combination repair is considered to be the best method of repairing a punctured steel belted radial. Some run flat tires also can be repaired. If you have a flat tire, be sure to talk to your local tire repair shop to find the safest options.