Markham is a plaza city. Retail and services cluster into multi-tenant buildings. The strips along Highway 7 and Woodbine, the plazas off Kennedy and Steeles, the towers around Downtown Markham. It's normal here for four clinics or half a dozen studios to share one civic address.
Google handles that with a filter. When it sees several listings at one address with the same primary category, it ranks one as the best match for a search and leaves the rest out. There's no penalty notice and no warning email. You just don't appear, while a business two doors down does. Owners usually assume their SEO is weak, when the real problem is that Google can't tell the two of you apart.
Getting out of it is mechanical. Distinct legal business names, separate phone numbers, separate websites where possible, and primary categories that don't overlap. The unit number does not help, so stop counting on it. Once the signals are separated, the ordinary work starts paying off again, and it pairs with a Markham web design build and the wider local SEO service.