I also do my own toenails in the summer but I'm not as good as a nail salon.
When I got my toenail fungus I was in a very reputable place that did a low volume of pedicures and had one or two nail techs that were spectacular. In my case, I think when she trimmed and worked around the big toe she clipped the nail on the side too far down and created an opening to the nail bed. After that, anything can get in anywhere. 3 weeks after that pedicure I had a full blown fungus on the big toe. I never had one before and never had one since. The only way I got it cured was to have the nail removed. Lamisil didn't even work.