Yes, it is ethical. The sales assistant isn't there to sell you on the product. They are there to sell you on buying the product from them. There are many ways that B&M stores can stand out from their online counterparts. Notably, they can help the customer make purchasing decisions. For many people, getting accurate information about a product and what accessories to purchase with a product is sufficient to shift their purchase from online to the shop in question. In other cases, the store can go further by providing the product immediately and by setting up the product for the customer. They can also highlight the support that they offer after the product has been purchased.

Of course, many of the people who want to portray showrooming as unethical want to gloss over those points. Many B&M businesses want us to ignore what the can offer above and beyond online stores because they want to hire low cost labour (who rarely understands the product) and that have returns and exchanges as their only form of post-sale service. There are, of course, exceptions. Then again, I'm not hearing many of those exceptions complaining about showrooming.

At the end of the day, I suspect that this is mostly a result of consumer expectations. They expect low cost products and have had businesses reenforce and expectation for low quality customer service. When they go into that major electronics chain or bookstore, they may see plenty of product but receive lackluster service and virtually non-existent support. If B&M stores want to survive, they have to change these expectations from consumers or switch to online business models.

Then again, I suspect the whole notion of showrooming is vastly overblown. While price may be a factor driving people online, convenience is also a significant factor. Shopping in B&M stores, only to buy online, kinda kills the convenience factor.