If you decide on a vinyl fence, you want to make sure that they only use virgin vinyl under the outer shell, not recycled. In most styles they should use six-foot sections instead of eight-foot sections, which will sag over time. If they use an 8’ section then the rails should be 2”x7”.   They should only use top quality vinyl, so that the exterior profile looks like wood, not plastic. When the concrete is poured into the postholes, it should top off six to eight inches below the soil line to avoid freeze damage in the winter. There should also be an anti-frost heave bar installed at the bottom of every post. There is a lot more to know about buying a vinyl fence, but these are some basic points that any contractor should cover up front. If he doesn’t, or has different answers, find a different contractor.