-Check for dents which are usually on the top tube.
-Seat post seized.
-Bad rust, usually around the BB.
-BB isn't stiff or loose.
-If the BB is clean in all the nooks and crannys, if people clean behind the chainring properly its usually a sign they take care of it.
-Check the rim walls for brake wear.
-Check that the rims are not only true side to side, but up and down too.
-Try to make deductions on the price for every error you find, that pretty much always works to give you a good deal.
-Look for wear on the drivetrain.
-Check all of the weld beads for any signs of,paint flaking/creases and/or cracks and check the wheel alignment as this will indicate if the frame is twisted.
-If there's paint chipping behind the headset on the top tube its probably been crashed and its bent, and on the rear check the wheel is in line with the centre of the brake and in the middle of the chainstays, if its not the frames been bent sideways.
-Check the headtube for cracks.
-Headset bearings.
-Headset warping.
-Steerer tube.
-Bars for bending.
-Rim dents.
-Check wheels for spoke tension and side to side play along with true-ness. Thats another one where if someone neglects their wheels, its probably not the only thing they neglected
-Where the rear triangle meets the seat tube.
-Brakes and hoses, and seals on brakes or forks.
-Have a good feel for oil or wetness.
-Also inside the steertubes for rust, and inside the headtube, and seat tube.
-Fork pitting, and cracks on the sanction bridge.
-Never buy a component or bike if it is wet.
-Have some sort of idea for where and how the bike was ridden. The owner might not be alright with you doing some of these things, but that might show either lack of confidence in the bike. Or it might not mean anything at all.
-Check all bushings/bearings for play
-Take the rear shock off (if it's a full suspension) and cycle the linkage through it's travel. It should be smooth and there shouldn't be any sticky points. If there is, the hardware will probably need replaced.
-Check fork stanchions for scratches and make sure the fork seals are in good shape
-Dropouts
-Dents in the rim. If there's too many or they're too big, they'll cause tires to blow off.
-Make sure there's grease everywhere it should be (seatpost, headset, BB, chainring bolts...). It's an easy fix if nothing's seized and doesn't hurt the bike too much in certain areas, but it'll tell you a lot about how the bike was cared for.
-If you're buying a classic or project bike that's older and has been around, it's not a bad idea to take it to a shop and check the frame alignment. Get your shop to blow compressed air through carbon frames if you're wary of them. Metals fatigue, and it's been said that aluminium bikes have a "shelf life" of 15-20 years. Obviously if your ride bikes hard they'll break, but metals get weaker with time.
-Always be cautious when looking at a frame that is freshly powdercoated. You'd be shocked at the ammount of cracked frames being hidden and sold on.
-Take the rear shock out and move the rear linkage through it's travel, make sure I is smooth with no sticking point, you don't want a warped frame.
-Check the chain guide mounts are straight. If they are bent or cracked the bike has been rag dolled and thrashed.
-Dents in the downtube are common on dh bikes but if you can still find one dent free.
-Never believe anything about a welded repair. Alloy has so many complex properties. Stay away from welded repaired frames, they will crack again, possibly fail.
-Stay away from raced frames, they may have been rag dolled down many a rocky hill, lots of stress on the headtube and links.
-Try and get the seller to deal with you on eBay. It may cost a extra 20 bucks but you will have buyer protection and gan get a refund if anything goes wrong.
-You should definately bring a rag with you as well... wipe down the fork and shock shaft and pedal it off a couple curbs at least and then check everything you just wiped for signs of oil
-Dont buy a bike from some random guy who offers to meet you half way in a service station somewhere. It will be stolen.
-Have a look around your surroundings when you go to a private residence but don't appear nosey. Ask yourself if they are genuine bike riders or not.
-Don't want to sound to stereotypical but take a look at the person who is selling, Is he/she is wearing a white matching shell suit or tracksuit, or has a staff terrier, sovereign ring, mobile phone hanging around their neck, trousers tucked into their socks, Baseball cap on back to front, - WALK AWAY.
-If the bike they are selling is stolen and you buy it off them then you can be sure that they will take your money before beating you up and taking it from you again to sell to some other poor mug. This applies more to the younger buyer.
-Save all the time and hassle and use eBay. Get buyer protection and when receiving the bike to your LBS to get it checked out. Any problems send it back within 14 days and get your cash back
