I'm not really a flipper but occasionally sell and when I buy I almost always have resale value in mind.
I get absurdly attached to my bikes, which is why I have so dang many of 'em. I just sold one of my old carbon frames on eBay and the buyer sent me back a pic with it built up. Made me feel good. Likewise I sent a pic of my refurbed De Rosa to the original owner I bought it from and he sent a very nice, heartfelt message back telling me how glad he is that it's in good hands. Makes me feel good about our sport/hobby.
I'm selling a frame now that I never even built up because it's too big but dang I like it and it's sat in my closet for about 6 months while I decided what to do.
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N = '96 Colnago C40, '04 Wilier Alpe D'Huez, '10 Colnago EPS, '85 Merckx Pro, '89 Merckx Century, '86 Tommasini Professional, '04 Teschner Aero FX Pro, '05 Alan Carbon Cross, '86 De Rosa Professional, '82 Colnago Super, '95 Gios Compact Pro, '95 Carrera Zeus, '84 Basso Gap, ‘89 Cinelli Supercorsa, ‘83 Bianchi Specialissima, ‘VO Randonneur, Ritchey Breakaway Steel, '84 Paletti Super Prestige, Heron Randonneur