There are many instances of hired techs installing back door spyware.
Make sure the person helping is certified and undergoes regular background checks. Also, even if you turn off your wireless feature and use wired connections, the router / firewall still needs to be secured properly. A web crawler could still seek to penetrate the firewall (like Stuxnet).
Sadly you’re right. Even the *ahem* techs *clears throat* at Geek Squad can have questionable credentials. Never use someone who advertises on a road sign or on a public bulletin board, IMO.
Your best bet is someone who works in the industry as an engineer or administrator who does more than answer phones at a help desk. That’s not to say that help desk people aren’t technically ethical or knowledgeable, but help desk is usually where IT people 1) start their career and/or 2) end their career. I worked help desk for 6 years and have been doing engineering work for 15. If you don’t have the drive to get out of help desk you’re either a masochist or lazy.