There are bookstores with knowledgable staff. I find that used bookstores are better than most. Ditto for specialist bookstores.

As for the word should, it depends what you mean. Researching at vendor A then buying from vendor B is certainly short-sighted. Vendor A is unlikely to survive unless people buy from them, so you should buy from vendor A if you want to receive quality service in the future.

On the other hand, talking to salespeople is not a legal obligation to buy. Businesses realize this, and most wouldn't have it any other way. Could you imagine how hard it would be to get potential buyers in the door if they were obligated to buy something? People would avoid stores that they thought had higher prices, and markets that depended upon impulse buys would collapse.

Price shopping is also the norm for certain types of vendors. Car salespeople are pushy because they know that most people are shopping for the best price. The sale has to be closed before the buyer leaves the lot or the sale probably won't happen. Why should other stores have different expectations from their buyers? The fact that these big box book retailers think otherwise is an indication that they've been free from real competition for too long. In that case, perhaps this comparison shopping with online retailers will push them to be more competitive.