The first thing to remember is that you are always charges by Google for ads in the arrears. You do not "prepay" for ads, you pay as you go.

Your first charge from Google will be a qualifying amount ($50) to establish that your card on file works. Then they will bill after your initial $350 is ad spend has occurred. Each payment thereafter will take place in $500 increments. 

Depending on your monthly target Google budget, you may see multiple $500 charges from Google on your credit card statement. A big part of our management service is to tightly manage to your monthly target Google budget.  If your campaign is pacing to overspend or spending too fast, we will pause or adjust the campaign to ensure you stay close to your target. You can always check your actual monthly Google spend by logging into your Campaign Analytics portal.