I take a pessimistic view of used pricing. Be wary of worn drive trains, lack of frame warranties, older geometries, older suspension design, lack of availability of suspension parts, older tech in general. OTOH, it is helpful to compare what you are buying used against what it would cost to buy the equivalent bike at new prices. Also watch for sellers who are overly optimistic about the value of any upgrades they've done over the years. Most sellers over-value their upgrades.