>Nah, Spur (a company tracking residential proxies) doesn't flag it at all.

I looked into it and so far as I can tell it works off a blacklist system, rather than any sort of automatic analysis (eg. TCP or MTU fingerprinting). If you set up a "residential proxy" in the form of a home VPN, it won't be detected. It also means the detection is only as good as whatever their backlist source is. If it's a niche provider, it might not get picked up at all.