The mere fact that there is a denial doesn't require an investigator to believe the denial.

If you have evidence that conflicts, somebody who sees all the evidence can make a determination as to which evidence is more credible.

If A sold the chips to B and B sold the chips to C.

If A says "I told B that they were altered"
C says "I bought the chips from C and he didn't tell me they were altered"
B says A never told me they were altered.

somebody needs to figure out which one was lying. I think Jim Reilly has the appropriate experience to do this.

But if B and C refuse to talk there is no reason to doubt A.