It’s a classic case which I am sure everyone experienced at least once, one way or an other. I mean, every agency is trying to get new customers and most of the time it’s going to be at the expense of an other agency. How easy is it to tell the customer: “i will do a better job and cheaper! ” If you’re a good salesman, chances are that if the client is not experienced (which seem to be the case here), he will catch the bait and try an other agency. My advice: if it’s a big account, give them the account and let the other guys fail. It will show them that you are 100% confident in your work, and that your fee /retainer is worth the work you are performing for them. Eventually, they will come back, and if they don’t then they won’t have anything bad to say about your company and practices. Next: update your contracts to cover such cases.