Whether a witness's criminal record damages his or her credibility (believability) depends on what their conviction(s) were for.  Ordinarily, if the crime did not involve dishonesty, it should not have much impact if any.  But there are other things that go into credibility as well, and it is often hard to tell how well a witness will be believed until after the trial.I would not be too quick to reject deferred adjudication, especially if your son's lawyer has recommended it.  The fact that your son is not actually guilty is no guarantee that the verdict will come out that way, and in the meantime his life will be affected by the open case and unless he has a public defender, a trial will run up a big legal fee.