It's not uncommon for a polycrystalline solar panel to give you at least 20 years of trouble-free service. The advantages of crystalline over amorphous panels also mean they'll need less maintenance and will stand up better in inclement weather.
The downside is that the manufacturing processes are more expensive and those cheaper prices seem to last just as long as the high cost ones. We recommend getting crystalline solar panels because it's likely they'll last you longer than cheaper alternatives, but we don't take responsibility for any misleading advertising claims made by retailers!