GC job is future job. Law only requires the petitioner to pay that wage after GC gets approved, but the petition needs to establish the ability-to-day from PD.
I don't think getting paid lower will be issue at 485 stage, and I haven't seen any 485 denied due to that. If CIS does that, it clearly violates its own law unless it can prove the job offer is not a bona fide offer. If that is the case, the denial is based on the offer not geniune, not how much the applicant gets paid. As long as the job offer is a geniune one, the difference between paid wage and LC wage won't be an issue.