The review default definitely gets their attention. If you use it, you must also have a clearly defined penalty. So, not only is it accepted ""after X business days"", but clearly state that support after that is extra. You can consider a ""$450 charge"" reopen the issue for diagnosis, and repair (the ""prescription"") might cost more beyond that fee. Do recognize this approach ONLY works if the project is completely prepaid. (We often break payment in two, with the final portion to be received BEFORE we do the final migration.)
We also use 3-level proposals. The length of time before we default to ""accepted"" is short on the cheap one and longer on the premium one. This, alone, seems to be a pretty effective lever to push them to the more expensive choice.