If it’s under a year old you’ve always got the manufacturer tech support that usually comes with these things.
As for replacing internal wi-fi cards they are actually generally quite easy (depending on the laptop model or course) as you’ll generally find them under one of the panels on the bottom of a laptop (the below photo is my laptops wi-fi card) and it is generally as simple as whipping off the panel, unplug the antenna (the gold connectors), unscrew it and remove, then just plug in a new one (the attached photo is the one in my laptop). That’s assuming of course it’s a hardware issue (something which a Linux Live CD would prove/disprove, Mint distro is usually quite good).
Alternatively you’ve also got the option of an expresscard wi-fi adapter (a few options to save on the limited quantity of USB ports a laptop usually have).
I’ve seen too many that stuff them under the keyboard or in some other harder to get to spot…
Yep! That’s been my experience. Either under the keyboard or even some other place inside that you need microscopic screwdrivers, four hands, a disassembly plan, and steel nerves to get to.