Used receivers in thrift stores, estate sales and auctions are generally overpriced and outdated.
I have seen many used or re manufactured receivers fail during classes that I teach.
If the hiker is in need of a back-up receiver here is what I would suggest:
· Keep an eye on the blog www.gpstracklog.com. The blogger keeps an up to date site on what is happening in the world of GPS receivers.
· Identify what models are of interest and then visit Ebay, Amazon and WalMart.com to get a price baseline.
· Get a relatively current model. For example, Garmin models such as the 60 or eTrek series should have the following nomenclature next to the model name such as H, or HCx (Garmin GPSmap60CX.)
· A receiver is in reality a hi-tech piece of equipment. If the viewing screen is badly scratched or the case is cracked or showing signs of rough wear walk away from it.
· Never buy a receiver without a demonstration. Take some AA batteries with you when you go shopping.
· The receiver should track satellites within a few minutes of being turned on and should be locked on, ready to navigate in 4-6 minutes (ball park estimate.)
· Determine how much mapping capability it has. For example, my old Garmin GPSmap60 receiver had the capability to store 100 mega bites of data which approximated to about half of the state of Oregon. Receivers with micro SD cards offer more capability.