Help? Agency Writing Off AdWords Expenses

Any advice on writing off AdWords expenses if you're running your own agency? Here's a example breakdown of how my partners and I are bringing in revenue:

• Client agrees to pay $1,000 per month for paid search campaign on Google
• We charge a management fee which is in addition to the $1,000. To make things easy, let's say we charge a 10% monthly management fee. Meaning, the client is paying us $1,100 total every month.
• From our business checking account my partners and I deposit $1,000 into the client's AdWords account that we're managing leaving us with $100 in profit.

Is it better to show $1,100 cash coming in to the business and writing off $1,000 or should we put the client's card on the AdWords account and invoice/collect only the $100 each month?
What are the pros/cons to each scenario?
I hope I made sense. Let me know if anything needs to be cleared up! I thank you in advanced for your responses.