why would an all-electronic part, that worked for 4 months, suddenly fail? If you trust the seller, you are getting a part for under $100 that you probably normally sell at close to $200, hopefully the extra $60 or so you pocket mitigates the risk. On my end, it may not be worth selling for like $30 or so, and with 2 new evolution stats, I doubt I will ever need a spare.
ALSO - you forget that homeowners also frequent this forum. Saving $50+ for a DIYer may be significant.