This report by the Denver Post suggests some impropriety at the Adams County Assessor's office, noting that some of Assessor Gil Reyes' biggest campaign backers received highly favorable assessments of their properties. While the article does a good job documenting the declining property tax burdens of some of Reyes' donors, it doesn't really make the case that something improper or illegal is occurring. To do that, the authors would really need to show that those who did not donate to Reyes were having a harder time getting favorable assessments than those who did.
That said, this does raise the key question of whether we need elected assessors -- or secretaries of state, or sheriffs, or judges, etc. --- at all. Does the desire for reelection assure accountability in such races, or does it create problematic conflicts of interest with little added democratic value? I have no idea, of course, but it would be nice to know whether elected assessors actually do their jobs better than those appointed by county commissioners.