The peer reviewers will be looking at the design of his experiment--could it actually show such a link, and does it control for other factors that might explain the result? Does the paper give enough detail for others to repeat the experiment? Is the analysis of the data sound statistically? Is the work original? Is it citing appropriate prior researchers?
Even in a fraudulent paper, those aspects of the paper should be OK. The fraud will generally be in lying about the results of running the experiment, which is beyond the scope of peer review.
Where that gets caught is after the paper is published, and other researchers try to replicate it and get different results.
And some of the scientists insisted on non-disclosure agreement before agreeing to help Amgen reproduce published results, which proves most papers don't publish nearly enough details to reproduce main results.
Peer review is a social organization that necessarily never lives up to its ideals. At top journals such as Science, Nature, Cell, editors also consider PR values, popularity of topics, exclusivity. It is standard practice to obtain prior favorable impression by contacting editors before formally submitting manuscripts at these places. There are different standards of peer review; consortium such as ENCODE and TCGA have a different track for their papers.