Someone who is "really a plumber" will have a Florida plumbing contractor license. You can verify that with the following link.
Licensing Portal - License Search
It doesn't appear that Gary Stambaugh has a plumbing license, but it may be listed under another name. If you want the job done by a licensed plumber, I would suggest you ask for their license number before they even come to your house. It is very easy to verify. I don't think that most self employed guys doing plumbing work in The Villages will be licensed plumbers, but you may find one.