word demand – Reverse to ‘online’ where ‘offline’ will not work

To highlight the contrast in between the operations through online stores and ones with physical stores, buildings, or facilities, you can utilize the term brick-and-mortar (also composed: traditional, physicals, B&M).

brick-and-martar
adjective
a brick-and-mortar company is a standard business that does not run on the Web

According to Wikipedia,

More specifically, in the lingo of e-commerce companies, brick-and-mortar organizations are business that have a physical existence and deal face-to-face customer experiences. This term is generally utilized to contrast with a transitory service or an internet-only presence, such as an online store, which have no physical existence for buyers to check out and purchase from directly, though such online services generally have non-public physical centers from which they either run business operations, and/or warehousing for mass physical item storage and distribution.

So, based upon your example sentence, one possible reword is,

Whether you have an online or a brick-and-mortar store, marketing is a crucial tool to boost your business.

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