As far as certs are concerned in the field, to me it shows you at least have an understanding of the issues at hand. Does it mean someone without certification doesn’t know what they’re doing? Of course not. Personally I hold my CompTIA A+. I do think their requirements for renewal these days are in excess but that’s beside the point, especially for something like the basics A+, Net+, or Sec+. All certification does besides make certification companies money, is show employers/consumers that you have been recognized as someone who knows what they’re doing. As far as you own it, you PWN it, I fully agree. If you own something it is your right to take it to where ever or whomever you choose to work on it.
Honestly, I think certification for manufacturer warrantied work certification is a necessity to avoid issues of multiple returns on items needing to be repaired because a “tech” didn’t do it the way it was supposed to be done and caused an issue with the device. By companies certifying technicians, it protects them and the consumer. Certification should be free for manufacturers but a test should be required and on a per manufacturer basis. Again to protect the consumer.
Now out of warranty repairs more power to you. Take them anywhere.