It should be based on the time, compression (if they claim good compression) and customer service/warranty.
1. Order placed on this date
2. Item received on this date
3. Claimed 100psi compression/ good compression
4. video proof of you opening the package and going a compression test on the spot.
5. Customer service, correct order received, etc., etc.
All on a scale of 1 to 10
or
to
or
if it's BAD!
If the motor loses compression between the time you received the engine and when install then you can't say it's the vendor's fault and vice-versa if you tape yourself opening up the engine and doing a compression test.