Wiktionary
showrooming
n. (form of gerund showroom English); inspecting merchandise in a physical store, then purchasing the identical product from an online merchant; using a physical store as a showroom for an online merchant. vb. (present participle of showroom English)
Wikipedia
Showrooming
Showrooming is the practice of examining merchandise in a traditional brick and mortar retail store or other offline setting, and then buying it online, sometimes at a lower price. Online stores often offer lower prices than their brick and mortar counterparts because they do not have the same overhead cost.
The reverse phenomenon of showrooming is webrooming. In webrooming customers research a product online and buy in a store.