The commercial market is very different from the residential one. Thus you should at the very least join a local brokerage that has clear evidence of commercial listings and sales.
On the other hand, although joining one of the Big Guys (such as Ellis) could help you locally if it enabled you to be a big frog in a small pond, it could also end up with your simply becoming a small frog in a large pond.
As in the residential field, one of the keys to success is that you can do and do do what no-one else is doing -- which includes doing it better, being more qualified to do so, and having the backing of an established presence/recognition in the market.
Duncan
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Acts as an Exclusive Buyer Broker for residential and non-residential properties in Canada's Niagara Peninsula.