I have talked with management at National Memorial Park on Lee Highway in Falls Church, and they do not buy back plots they have sold to anyone. They recommend selling via classified ad, such as Craigslist. You can, however, ask them how much the plots in your section are going for, to help you price them fairly. Plots do not depreciate.
These listings are separate to the general real estate listings for properties. That site is specific to cemetery plots. Please contact me if you are wishing to buy or sell residential real estate =] Cheers.
List it, SOLD!