There is a gamut of things to consider when you go to buy furniture that is pre-owned. These have mainly to do with quality and the condition and being able to recognize you are getting a decent shake. Much will depend on your budget but before even leting price into the equation, look at:

• Makeup of Wood vs. Particle Board/Fiberboard and Veneers.
  Clearly there is no substiture for authentic, solid wood. This is a major benefit in buying used, your chances of getting the real tend to leap, which is also inherent with price. While used furniture orginating from later years has been made from particle board. As a precaution though when determining whether particleboard has been used is always not so obvious, give some of the more artful laminate reproduction techniques that have evolved in furniture manufacturing. The less desired, particle board construction, put out to serve the lower end of the market, might be indicated by a bubbling on the surface, signs of exposure to conditions of high humidity, moisture, or water. In more severe cases resulting in swelling. Too, the density of particleboard tends to loosen around screw holds and points of stress. When the composition of the underlying wood or board is not so obvious, check for yourself the end-cuts found at side panel bottoms, and shelf ends (remove the shelfs to see) and drawer ends. Although having attained such common and widespread usage, particle board does offer some environmental benefits like for material recovery, and economies . But in all fairness, durability of this furniture relies on the quality of the outer laminate and the production methods of adhesion of this layer -- true laminates offer improved durability, thinner vinyls are troublesome -- both are difficult to repair.
  
  The fiberboards are another material to look out for when buying used furniture. These are pressure treated amalgamations of sawdust and wood chips. Referred to as MDF - medium density fiberboard and HDF - high density fiberboard, fiberboard composites are typical among visually accessible panels; notorious at rear bookcases, etc.
  
  Veneers, these slim wood layers, are a somewhat happy medium between the laminates and real wood. They help preserve natural resources although they are not as repairable as real wood.
  
  Whatever the type of wood/artificial substiture, view all resting places on the furniture being considered and elsewhere, for common wear and abuse patterns, marks, or hopefully a pleasant surprise.
  
  
• Joinery - dovetail joints are the sturdiest available but mitres (angular perimeter cuts) and mortise and tenon joints (chiseling hollow or cutting through) all reveal quality craftmanship. Economical solutions rely on securing by dowel(s), cams, by direct screws & straight glueing.
  
  
• Slide Tracks & Drawers - expect older tracks like for the drawers to be rudimentary, providing rougher operation than metal and plastic rollers. Tracks that slide on bearings glide freely and endow long life when is noticable on every slide -- operate all doors and drawers for yourself.
  
  
• Hinges & Door Hardware - doors should swivel on a smooth course without hints of bumping. Any hinges or hardware, in need of replacing, might be available at major home centers like Home Depot who carries a limited range of such hardware. For refined searches, check your cities builders hardware. The door and drawer pulls are the simplest part to modify, buying new ones can assimilate a questionable piece of furntiure into your existing decor. If you are not confident that a permantly mounted hinge that is conspicuously morticed into the wood, cannot be matched, don't buy the furniture.
  
  
• Legs/Cross Bracing - Grab each of the legs and braces and check for fit that should be firm and without wobble. If it does wobble though be aware that this isn't necessarily a downfall for an aged piece, however. Correcting this involves the skills of the local furniture shop, or, if you are confident with basic carpentry skills; gently knock the component pieces apart, clean out and sand the post/recess areas the come in contact with the failed glue bond -- and then reassemple with quality wood glue like Titebond, securing with cloth web clamps.
  
  Normally a specialized request for other stores, the cloth clamps are available at Rocklers Woodworking (an indespensible resource for furniture repair) and are reliable tough nylon, a cinch to tighten and loosen, and these handy straps have corner guides through which to distribute the hold. They are reasonably priced at $6.99 each when on sale and extend to 15' lengths, making them suited for larger cabinets and dressers as well as the simple chair..
  
  - Legs that are corner blocked preferred.
  
  
• Fabric/Upholstery - the removable covers are best, zippered for the cushions. Set in the seat, lay your arms about the handrails. Test the firmess that it meets to your liking; there should be a consistency of firmness. Search for signs of internal support like from extending springs or slats underneath.
  
  
• Framing - kiln-dried hardwood is optimal. The amounts paid should be set for softer woods accordingly.