It sounds like someone is going to have to do the work, so...
1. find out the first EC's phone number to discover if he is being paid, and that the issue is not he "failed" inspection. Always, always give the other EC the consideration when being asked to follow another EC.
2. If you find out the call by the customer is legitimate, then discuss over the phone before you go waste any of your time that the cost may be more than discussed earlier, as there may be some remediation adding to the cost. If they are not happy with that discussion, say thank you and go on your way.
3. If they decide that you are to do the work, ask for at least 50% of the total cost to sign the contract, with the balance due the day of completion of the contract work (I hope you have a contract signed before you start the work).
File the job and good luck!