I had a nail in my tire that I attempted to plug myself. After struggling to get the plug in I decided to just take the tire off and bring it in for service. Dropped it off at Discount Tire in the afternoon and told them I would be back at noon the following day to pick it up.
When I went back expecting to pick up the tire, the same guy told me that there was a problem and that he would get the tire and show me what it was. There was a tiny bit of residue from the plug I tried to get in there around the hole. Tells me that they can't work on it because it wouldn't be safe. He would gladly sell me a new tire though.
Ended up going to Goodyear and they fixed it for $20 in about an hour.
What really irked me was that they had hours to call me and let me know they weren't going to even attempt to fix the tire and I heard nothing. I used to go to this place because it was convenient but never again!