Hello,

I have had two of my sites members receive duplicate charges on their subscriptions due to my dev site.

@Terabyte has added this to the constraints before to prevent this: 

However its not working. Payments are being duplicated.

The easiest solution is not to use cron.  You could also swap your merchant API keys to use a dev API key on your API site.  

Ideally, delete those gateways entirely (unless paypal. Do not delete that as it will remove payment profiles on paypal itself). 

Removing cron is also a good idea, as mentioned, but of course that will not stop things entirely.

I would ask if you are using commerce on your test platform? If not, you could also remove it entirely if needed.