So you have a small yard and only need a push mower to cut it instead of a self-propelled or rider. That simplifies things immensely and with these tips it will help assure that you get a good one.
I have been a push lawn mower repair technician for over 5 years and from that experience I can tell you what to look for and tests to do when looking at your prospective used push mower.
First I would stick with the major brand names of engines. Briggs & Stratton, Honda and Kohler are the most popular although you probably won’t find a Honda engine on a push mower. More than likely it will be a Briggs and Stratton which is perfectly fine.
For the most part the decks, handles and controls are basically the same. The deck will be a stamped piece of metal but it could be a welded deck. Welded decks are much heavier and will last for a long time.
The engine should start on the first or second pull. If it doesn’t, that is a good time to move on. If the push mower has sat for an extended period of time, it may not start on the first or second pull so take that into consideration.
Check the engine for any oil or fuel leaks. Check the engine oil to see if it is black and the quantity of it. Is it low on oil? Black oil is a sign that the engine was probably not maintained as well as it should be. Is the engine dirty or have spots of grass stuck to it which would indicate an oil leak? Grab the engine (after it has cooled) and try to move it around to see if there are any loose mounting bolts.
Check the control cables for fraying and ease of operation. Does the safety bail spring back or does it slowly retract. It should spring back after you release it.
Pull the spark plug boot from the spark plug for safety and look under the deck to see if there is rusting or if there is a large buildup of grass under it. Wet grass will lead to rusting of the deck and it can rust completely through.
Check out the blade for straightness and sharpness. Is it worn out or worn down and needs replacing? Are there any big nicks in the blade that would indicate it struck something?
Lastly, roll the mower and pay attention to the wheels. Do they spin freely? Are they leaning outwards or inwards? Are they broken or the tread is worn down?
If you suspect anything that is not quite right about the push mower, ask the owner to clarify what service work has been done. They may or may not know or choose to not answer your question.
I hope this arms you with enough information to make a good informed choice in how to buy a good used push mower.