Give your users something like "first two weeks free", which will annoy the fraudsters who want the charge to go through immediately.

but then doesn't that require you to hold onto the credit card details to process two weeks later. One of the attractive features of stripe is that you don't store cc details on your system but rather they get passed on directly to Stripe. if you implement a delay, you have to hold the credit card to charge later

No, you tokenize the card through Stripe immediately and then charge the token 2 weeks later. You don't have to hold on to the card details.

so after you charge the card two weeks later, the transaction still gets completed unless you've somehow figured out during the two weeks how to determine whether \the attempt was fraudulent. I don't think this strategy will work because it will depend on the fraudsters knowing that the payment won't be processed for two weeks and then deciding it's not worth it. Are they going to read the TOS?

If the UI makes it clear that they aren't charged for two weeks, they likely won't bother waiting and move on to target a different service.

they also might see an advantage in the delay that you don't see and try it out.

It looks like Stripe can defer payment for 7 days:

https://stripe.com/blog/auth-capture

That's quite clever.