I'm sure if you would have bought your EOtech from someone who was selling it at full retail, they'd have exchanged it for you.
The reason places like SWFA can sell you products at far below retail is because they cut costs by not stocking a lot of extra product for exchanges. That, and high sales volumes, allow them to make a profit while selling at a price few others can match.
But you must realize that TANSTAAFL. If you are saving money, there's a REASON. In this case, the reason is because the buyer must handle problems with the products himself, via the manufacturer.
SWFA actually has much better customer service than you'd expect for the prices they offer. But when you shop around for an item purely on price, you need to have a realistic attitude about the level of service you can expect to receive for that low price.
-Troy