[Sirrotica]

Since you can't hear it run, or test the transmission, I would offer core prices, and assume both pieces need complete rebuilding.

$100 for the engine, and $50 for the transmission.

I know, "It ran perfectly before we pulled the engine", heard that line way too many times in the past to believe it.

My rule of thumb is core value, unless I can hear it run, or drive it to test the transmission. Even when buying from a junkyard that warranties the engine, or transmission, few places will pay the labor to R&R the parts once in the car, and finding that the part in question is defective. They'll give you another used part, but usually that's as far as the warranty goes.

I made my living for 40 plus years repairing cars, and same as "shipping isn't free", when buying online, labor to R&R defective parts isn't either.

In this case if you found out the part wasn't as good as described, they don't have another unit to give you to make you whole. And good luck getting any portion of your money refunded on a private transaction.

If the seller will allow some disassembly for verification that the used part may be what they claim, then the price can be adjusted. Most people won't allow you to do that though.