I owned a deli in in Gilbert AZ,and Quiznos for 6 years before that. When you buy certain products, meats, veg and the like, you will pay by the pound. The distributor will use the term "catch weight". When the manufacturer packs the case, they will afix a label to the case indicating the actual weight of the contents inside the case. That tilapia is indeed sold by catch weight, we use it in one of our resaraunts (a buffet).
$3.99/lb for Beer battered Tilapia is an ok deal, but not great, we are paying around $2.80/lb. If you were looking at owning a restaraunt, or already do, you might want to consider signing on with a major distributor if you allready havent. For instance, Cysco, US Food, Roma, Shamrock etc, a couple of these are local to me. You will likely have local distributors in your area as well. If you don't want to make a commitment to a major distributor, check out Costco business centers if you have one locally. Some of the prices on the flier you posted a link to are pretty good, the dairy and drinks especially, meats and seafood, not so good.
Though a couple of the cold cuts were ok/good prices, they were likely lesser quality. A very common tactic used by manufacturers is saturating the meat with moisture, adds weight but of course impacts flavor as well as shelf life. When the water evaporates, the product will lose visual apeal. For instance check out the ham product in the lower left corner of the flyer....you really will want to do your homework , fortunately, alot of manufacturers have representatives that will provide samples so you can tailor your menu to your spec.