What are credit card terms for paying for things like this? If you see your monthly stamps.com charge that you signed up for online and didn't knowingly opt-into, see it requires a business hours phone call to cancel, can you just dispute the charge at your credit card bank and let them fight it out? That would mostly leave you one place to look for charges, and one entity to talk to about it. Sure, be vigilant, but when something slips though, is that always a valid option?
I know my bank lets me dispute individual charges online. Don't have to talk to anyone. I'm not sure how it applies to these dodgy services that I may have technically signed up for. One thing I know for sure is that having someone like stamps.com deal with a credit card bank is way more painful for them than dealing with me. Easier on me and harder on them is a win-win.