A friend of mine blew a transmission in his immaculate Honda that he did not want to part with. To save money vs installing a brand new transmission, he bought a "guaranteed" trans from a wrecking yard. Then paid about $1,000 to have an auto shop R&R the "guaranteed" trans into his car.
Within 1 day, it was obvious the "guaranteed" transmission was faulty. Didn't shift correctly, and developed a bad leak. When he contacted the junkyard, they said: "no problem, bring it back and we will exchange it for another 'guaranteed' one."
I had that happen with my last Dakota... except that it was a brand new Dodge transmission. It worked fine until the weather got cold, then it wouldn't climb a hill until the fluid warmed up. Trouble is there are hills going either way after leaving my house. I'd drive back and forth in front of my house for 20 minutes before I could leave the property.