I'm looking at buying a gas-powered lawn mower from a friend, but I'm concerned because the mower was purchased new almost 13 years ago. How can I evaluate its condition and know if it will last me several years without any major overhauls? Of course certain parts like the blade are designed to wear out and be replaced eventually, and I'm fine with that. I just want to make sure I can keep this thing running for a good long time. I'm also worried about the continued availability of replacement parts.
I'm assuming that you trust your friend and he'll give honest answers when you ask the following questions. In general if you're buying it from someone you don't necessarily trust, you'll probably want to inspect it and let your eyes tell you if they agree with the answers. (See below.)
A "no" to any of the above takes some life off the engine.
Give the machine a visual inspection:
My experience with an old machine -- a 1970s-era rototiller -- is that replacement parts have been easy, but I've only replaced belts, spark plugs, and the pull start rope.