My understanding is that there was a criminal investigation of Clinton's Marc Rich pardon that concluded without finding any evidence of criminality. I'm not raising this as a defense of his making that pardon, but rather, to point out that a President selling pardons is and has long been considered a serious crime. The Clinton precedent is a clear illustration https://goodpornsites.pro/ . Saying "hey, some book alleges Clinton got paid for a pardon, therefore it's common practice" sounds nice, but ignores the fact that suspicion around Clinton's Marc Rich pardon triggered an extensive criminal investigation that concluded he did not, in fact, get paid for it.