As legacy systems begin to experience issues, there is a growing need for used and refurbished modules. Today, several vendors will either purchase your used modules or facilitate resale through an online marketplace.
It is far better to repair older systems and keep them running - rather than prematurely replacing an entire site - as another important way to minimize waste.
There are laws on the books about reselling used equipment. We are not attorneys, so we cannot hold ourselves as experts on the topic. Be sure to look into resale regulation & requirements before you start advertising your used equipment.