Take a look at the club head for signs of wear before you buy it. A worn spot on the club head where the ball strikes will prevent the ball from making good contact and affect the performance. Grooves that have defined edges on the face of the club show that the club still has some life left in it and has not been completely worn out.
Check the shafts of the clubs for worn areas or indentations. Look down the shaft and make sure it has not been bent or twisted. You can test the torque by twisting the grip and the head in opposite directions. If you meet very little resistance while twisting, then it is a sign of shaft weakness and should be avoided.
Choosing between a graphite and metal club should be determined by your own preference. What type of club you play better with should be the type you choose. Each person has their own favorite and when buying used clubs, you need select the ones that are best suited to you.
Alloy clubs such as aluminum are great clubs but for buying used they might not be such a good choice. Alloys are more susceptible to wear than those made from metal. Alloys can be a bit cheaper to buy but since your buying them used, try and stick with metal clubs.