There's an ongoing debate among IT professionals when it comes to the best solution for a computer infected with malware (viruses, spyware, adware, etc). The traditional thought has always been that "mission critical" systems (computers responsible for running anything that plays a part in keeping people alive, vital infrastructure, and other super important tasks) should be formatted (everything deleted) and reloaded with their respective operating system, because that's the only way to guarantee you're deleting every last byte of infection.
Home PC's are supposedly OK to go the easy route and perform targeted deletions for the specific trouble-making software, aka relying on anti-virus software to find and remove everything, and leaving the rest of the files alone, because the risk of loss if the system is still compromised is relatively low and it's usually a lot faster and definitely cheaper.
The nuclear option
Sometimes I refer to formatting and reloading a system as "the nuclear option" because while it is guaranteed to fix certain issues, it also comes with some downsides. Some techs even frown on it because you're not actually finding and fixing the issue, you're just wiping everything out and starting from scratch. It's the same as having a hard to locate plumbing issue in your home, and instead of spending the time to locate the specific source of the trouble, you just light the whole house on fire and re-build it (after removing all of your valuables of course). I've always been a big fan of the method because if done correctly, you end up with a computer that not only doesn't suffer from the original issue, but now runs as fast as it did when it was new, sometimes faster, because we don't reinstall all the extra "bloatware" that came with the computer.
Targeting the issue
I don't want to make it sound like using antivirus software and manually targeting and removing the malware is a terrible option. If done by a qualified tech with enough experience, they can erase every last trace the malware snuck in and leave you with a safe system. In fact, I have a lot of respect for techs who are actually capable of reliably cleaning a system without formatting it. The problem is, in most cases I run into the tech was more interested in getting onto the next job and they don't take the time to actually verify the system is clean. They simply run a few popular antivirus/antimalware programs, restart the system, and if nothing grabs their attention right away, they call it a day and hope everything is good to go.
You get what you pay for
A lot of computer repair shops want to sound competitively priced, so they advertise rock-bottom pricing for virus removal. I've seen it advertised for as low as $30. I'm sorry, but the reality is unless you're OK with making below minimum wage, you just can't take the time necessary to properly clean a malware infection and verify a system if you're charging so little. If someone said they could change your oil for $5, the price might look great, but you'd know they were cutting corners somewhere to make that possible.
Everything device is mission critical to the person using it
In a world where computers are used for shopping online, paying bills, and banking has become an everyday task, every computer is "mission critical" to the person using it. The potential for loss if a malware removal isn't properly executed exists with virtually everyone's device. I know some techs don't agree with me, but I don't think it's worth gambling with the potential for identity theft just to save a few bucks and a little bit of time. There's huge demand for your stolen data, and enough cash on the table to rationalize huge investments in money and time coming up with ways to get it.