The reason a used tool is cheap is always the interesting part. Sometimes it is because a contractor switched platforms and dumped everything. Sometimes it is because the tool is one hard job away from the trash. Learning to tell those apart in about ninety seconds is the whole skill.
Start with the housing
Pick the tool up and look at three places before anything else.
The battery foot. This is where drops land and where plastic cracks. A hairline crack there means the pack will wobble, the contacts will arc, and the tool will start cutting out under load.
The area around the trigger. Cracks here suggest the tool was pried, dropped hard, or opened by someone who did not have the right screwdriver.
The vents. Caked concrete dust or metal filings mean the motor breathed the same thing. Wood dust is normal wear. Metal grinding dust in a drill is a short story with a bad ending.
Then the switch
Squeeze the trigger slowly through its full travel with the battery out, then with a battery in if one is available. It should ramp smoothly, hold steady at part throttle, and stop cleanly.
A trigger that jumps, stutters, or only works fully depressed is a variable speed switch on the way out. On many tools that switch is the single most expensive serviceable part relative to the tool's used value, which usually turns a bargain into a project.
Chuck, collet, and business end
On a drill, close the chuck on a bit and check for wobble by eye while spinning it slowly. A little runout is normal on a keyless chuck with some age. Visible wobble at the tip means the bit will walk and holes will be oversized.
On an impact driver, put a bit in and pull. A worn detent will not hold under load. On a circular saw, check that the shoe is flat and that the bevel and depth adjustments actually lock. A shoe that will not lock is a saw you cannot trust for a straight cut.
Battery contacts and the packs themselves
Look at the terminals on the tool and in the pack. Clean brass is good. Green corrosion, black heat marks, or melted plastic ridges around a terminal mean high resistance and heat under load. That is a walk away, on both the tool and the pack.
For a battery, weight tells you something. A pack that feels light for its rating is worth suspicion. Swelling that keeps the pack from seating cleanly means the cells are done. There is no home fix for that worth attempting.
The platform question
This is where people lose the most money. A tool is only as good as the batteries you can still buy for it. Before agreeing on a price, ask two questions:
- Is this battery system still being sold new?
- Can I buy a replacement pack from a normal retailer at a normal price?
If either answer is no, the tool is a paperweight with a countdown on it, no matter how clean the housing looks. Orphaned platforms from the last two decades fill flea market tables every weekend for exactly this reason.
The price math
The number that matters is not list price. It is what you would actually pay to get the same capability today, which for most tools means the current bare tool price plus the packs you already own.
A fair way to run it:
- Start with the realistic replacement cost of the bare tool.
- Subtract for cosmetic wear, missing case, missing side handle, missing depth rod.
- Subtract the cost of anything you know you will have to replace.
- Subtract more if the model is more than a couple of generations old, because parts availability shortens.
If the asking price still looks good after that, it is a deal. If it only looks good compared to the highest price you found online, it is not.
The quiet advantage
Buying used well is mostly patience. The same models come around again. Nothing about a tool that is wrong today gets better because you bought it in a hurry.