The three rules
1. IT NEVER HOLDS THE CARD. It can find the thing you want to buy, fill the basket and draft the order. You are the one who presses pay. The moment it can spend without you, a mistake becomes a real mistake.
2. GIVE IT A SPENDING ACCOUNT, NOT YOUR ACTUAL ACCOUNT. If something has to be automatic, let it have a virtual card with a small balance and a limit on it. Never your main business card, never your bank login.
3. READ WHAT YOU'VE AGREED TO. Some agents retry a failed action, and then retry again. Three attempts at one order can mean three charges. Know what it does when something fails before you let it act.
The other rules worth keeping
4. ONE CARD PER TOOL. If each agent or subscription has its own virtual card, you can see what each one spends and cancel one without breaking the rest.
5. SET A LIMIT PER PAYMENT AND PER MONTH. Most virtual card providers let you set both. The per-payment limit stops the single big mistake, the monthly one stops the slow leak.
6. TURN ON A NOTIFICATION FOR EVERY PAYMENT. If you only find out at the end of the month, you have lost the chance to stop it.
7. CHECK THE ACTIVITY LOG ONCE A WEEK. Five minutes. Look for anything it bought that you would not have bought, and anything it tried twice.
8. CANCEL THE CARD WHEN THE JOB IS DONE. A card for a finished project is access nobody is watching.
Keep this before you connect anything to payments, and send it to whoever runs your accounts. They are the person who finds the double charge, so they should know the rules too.