I handle high single-figures of these adware and/or potentially unwanted programs (PUPs) infestations every week.
Mostly it's Windows 7 and 90% adware/PUPs-centric, occasionally ransomware. In the huge majority of cases, the following will get a computer back up and sorted in a sensible amount of (billable) time:
First, bring known-good copies of AdwCleaner, Junkware Removal Tool, RKill and ComboFix on a thumb drive. Same-day downloads are preferred as some detect out-of-date versions and don't play nice. Shut down computer. Restart in safe mode with command prompt. Run explorer.exe from command prompt. USB typically works as usual, even in safe mode. Run each of the applications above as administrator in the order they are listed. Some will require a reboot to complete their work. The reboot should be in normal mode, subsequent restart(s) to run other cleaner(s) should be in safe mode with command prompt. Diminishing returns will take place after the third of fourth cleaner, and allow 15 minutes for a typical infection.
The longest it's taken me to completely clean a computer of was 7 hours, comprising around 18GB of tat. If it's a severe infection, I will recommend a rebuild from known-good factory media after a Windows Easy Transfer export, assuming there's not too much in the way of user content.
As an up-sell, I also offer a better-than-factory reset where there's a clean Windows 7 installed and no vendor-specific junk on there. Computer vendors aren't as bad as free-to-use software vendors, but there's a reason why a adequate Lenovo laptop can be bought in the UK for 230GBP (including sales tax at 20%). Install, updates, and Windows Easy Transfer will typically be around 2 to 3 hours. It's a hard sell with a cheap laptop, especially since some clients are already preparing to buy a new laptop rather than fix the old one.