I've got a client who had previously begun a PPC campaign before hiring my company to do it for him. The client insisted on knowing the PPC logins (since they were his to begin with) and for a time did not interfere with my company's work. Recently, however, he has started entering the accounts and making changes that are NOT in his best interest.
Has anyone else had this problem in the past? What did you do to deal with the issue while maintaining them as a client?
Yes, we've had that issue many times, and it really just comes down to clear communication. We tell clients "Here's why we need tactical control over the account and what you get by giving us that." We also tell them what things they can and can't do on the account, which helps them feel in control.
It's a big issue, though, and sometime's the best you can do is keep track of everything so that if/when the client screws things up you can have a clear trail of who did what.
You need to find the root cause of why he's meddling. Does he think he's knows best, does he want to be a position 1 for a certain keyword, or is he just bored with his other work? Ask him and address the issue.
Sometimes if a client hands over management to an agency, they find it hard to let go. 'My Change History' is your new best friend!
Make it quite clear that if he continues to "meddle" you can not be held responsible for any negative effects of his actions. Your company has done a lot of work to build up the campaigns (presumably you hvae been paid for your services?) and you would hate to see the progress destroyed by some tweaking that may not be in line with the overall picture.