When the manager of the food store checks the totals a second time, he looks at the wrong registers. He looks to the register on the right for the D'Arcy's, and the left one for the Bundy's. When they emptied their carts for the first time, the D'Arcy's had the one on the left and the Bundy's had the one on the right.
When Peggy is racing down the aisle to the checkout after Al has already won the competition, the grocery cart is missing the long knives at the front of the cart. When Peggy comes out of the aisle towards the checkout, the knives are back on.
The photographer actually takes a picture of Al's back for the promo shot.
Jefferson is forced to use a regulation shopping cart in the contest. The first time he uses it, Jefferson blatantly rocks it back and forth to make it look like it has wobbly wheels; in later shots the cart rolls smoothly.
At one point, Mathers takes fifty cents out of his pocket and tells the children to "take it; it's all I have". But he was paid in cash for his appearance at the market only a few minutes before....
When Al rolls a turkey on the ground to knock Jefferson and Marcy down, Jefferson's harness is visible.
When Marcy picks up an armload of egg boxes, you can see that there aren't actually any eggs in the boxes.
You can see Jefferson move his foot to allow the shopping cart to pass when he's lying on the ground.
Marcy mentions that she has lived next door to the Bundys for 5 years. But it's actually just been 4 years since she moved next door. The pilot aired in April of 1987 and this episode aired in April of 1991.