Bechorot 37 - Blemished Firstborn Animals Nowadays
If a firstborn animal cannot be brought as a sacrifice, either because there is no Temple standing, or because it was born outside of Israel, a panel of three laymen can examine an obvious defect and authorize the slaughter based upon it. Obvious defects include a blind eye, a cut-off limb and other similar ones, and the examiners must be somewhat familiar with the laws of firstborn.
If one sells the meat of a firstborn without showing its blemish to an expert and the buyer eats some of it, the seller is penalized to refund the full price, and the rest of the meat is buried. Similarly, if one sells beef and it is found to be non-kosher, but the buyer already ate some, the seller refunds the fulls price. In general, this rule applies to anything that is considered disgusting, such as non-kosher meat or forbidden seafood, because the buyer would rather not have eaten it. However, if the food is prohibited only by a Rabbinical decree, the buyer cannot claim refund for what he already ate.
Blemishes qualifying for slaughter include ear notched in the cartilage but not in the skin, ear split, punctured, and dried up.
Art: Edward Ladell - Shrimps, a peeled lemon, a glass of wine and a blue and white ginger jar, on a draped table