I actually have had people be condescending to me as well. I've found it simplest to just say - sounds great! Could we try X first? I'll pay. Oh, that worked, cool!

Even better, if it doesn't you haven't annoyed someone too much who now has to do the fix they suggested.

Flip side - union workers at some telecom co's are hilarious -

me: "why are you here?" them "I don't know, they told me to roll the truck." me: "OK - but this is a software thing and they fixed it online yesterday?" them "OK - I'll sit in my truck for 2 hours reading. Can I run some diagnostics after that so it logs my visit as a success?" me: "Sure!"

Reality though - I love that they actually send someone - because then if it is not fixed yet it tends to get fixed if their guy is sitting there!