[Nextgrid]

> they can submit basically any transaction they want at any time

This can be generally be accommodated in my suggested model, they just have to specify upfront how much & how often they'd want to charge. If the gym membership is 50 bucks a month, then the token has a monthly limit of 50 (or maybe a bit more, to account for potential extras). The token lifetime could be set for the membership duration.

> car rentals

Get 1 token with your rental fee + a separate token (scoped until car return date + some time to inspect/discover any damage) for the deposit amount?

[sidewndr46]

You're thinking technical solutions to a sociological problem. Businesses like this are built on the fact that they can charge you an unspecified amount for an indefinite amount of time. Any attempt at a technical solution means those businesses refuse to adopt that solution.