2010 Rav4, 170K miles, connecting rod noise

Was looking at buying a 2010 Rav4 with about 170K miles. Looked pretty good aside from needing new rear wheel bearings. Wanted a mechanic to take a look, so the seller dropped the car off Wednesday night at a local mechanic’s for a Thursday morning check-up. After sitting out all night there was a rattling noise in the engine in the morning on startup—very brief, then seemed to go away. Mechanic is 100% sure it’s the connecting rod. He said to me: “I don’t know if this engine will last 5000, 10000 miles, or more, but it’s going.”

Haven’t dealt with such a serious issue but this was a bummer after investing a lot of time in this car (good though, if we indeed caught a serious problem problem). Seller and I had been talking about selling for $4.5K—seller is now willing to go down to $4K. My priority is something reliable though, so think this is too much of a gamble.

Any thoughts? Any similar experiences?

Trust your mechanic.

I do! Even 4K feels like a huge gamble so I'm leaning away from it... More am curious for similar situations/engine rebuild experiences/etc