What most people get wrong
Treating reviews as a section the site should have rather than as evidence placed at a moment of doubt. A visitor hesitates at a specific point — the price, the form, the button — and that is where the evidence belongs.
The second mistake is one enormous block. Three relevant reviews next to the decision beat twenty in a carousel elsewhere.
Badges versus sections
A full section suits pages where the visitor is evaluating. A small floating badge suits pages where they are doing something else — reassurance without interruption, and it travels across the site rather than occupying one page.
Testing it
If you can, measure. Reviews near a form or a button produce a measurable difference in completion often enough to be worth the fifteen minutes of setting up the comparison.