I'm attracted to older, used garden tools because of their quality construction and their low prices. Old garden tools with metal parts were often forged from one piece of solid metal and then attached to solid wooden handles.
The trick to buying secondhand garden tools is to look for solid construction on welded points and pay special attention to where the metal attaches to the handle. If a tool has parts that are supposed to move, make sure they do. Another thing to look for on metal is heavy pitting and flaking, which weakens the metal so that the tool would be better suited for decoration than garden work.
Look for wooden handles made out of ash or hickory wood. Ash is a lighter-weight wood and not as tiring to use for garden chores. Hickory is heavy and durable, and was often used for short-handled tools. Check that the wood grain in a handle is straight all the way down. Inspect for cracks, past repairs and rotting. Watch out for handles and metal parts that are painted. The paint may be covering up cheap construction or damage.
Where can you buy used tools? Flea markets, garage sales, auctions, estate sales, barn sales and secondhand stores are good places. The prices can range from $1 to $40 for most used hand tools; very old, large, handcrafted, wooden tools can cost more; but you can usually buy common tools for less than $15. Happy hunting; the used garden tools you need are out there.