When we were working for one of the world's largest oilfield service companies, they overpaid us by $80,000. [The accounting group was paying the remaining balance on budgets, not the amount due.] I spoke with my contact who informed the accountants. The next month they overpaid us by $20,000. After that, the error was corrected.

Yesterday I received an unexpected check for $1500. I noticed the enclosed invoice was from Career Builder, another company, not ours. I immediately informed my client and returned the check. Complete honesty reinforces your credibility and your client's trust in you.