Was the price listed in the store $16 for the screen protector? If so, and you purchased it, that's what you agreed to. Online pricing often differs from instore...and that's not just with VZW...Wally World does this as well as many other stores. Sometimes it pays to look before you leap...
Typically, I tend to research my next phone well ahead of time and if I buy the phone online or in store depends on the cost since they differ. I go ahead and get any accessories on amazon or ebay (depending on shipping times) so that I am ready when I get the phone, since the phone is the only piece of the whole that I cannot do much in regards to the price. As far as what is online and what is in store, online will have sales sometimes or clearance. The store will try to sell full price every time.
a) you did not price compare
b) Verizon knows people impulse shop and don't price compare.
c) easy profit
really this this shocks you? You go to best buy, get a new TV, guess what happens when you buy an HDMI cable from them with the purchase. Yes, you pay 8x more For the cable.
Yeah, the profit in selling anything lies in the accessories. I used to sell computers and printers and such in a big box retail store. Lost $45 profit for each laptop sold and needed to attach a product performance plan, case, optimization and protection software package, as well as Office and anti-virus to make a profit. I could also attach a printer to the laptop, but then i'd need paper, ink, PPP, and a usb or networking cable attached to the printer. All that to make up for the hour I was paid to sell a few items and keep the lights on etc...