A lot of business owners believe that just because the previous business in this same location was very much like theirs, they obviously don't need to worry about a Zoning or Code Review. Sure, it might be nice to avoid the extra costs and delays, but you should know that even if you buy an existing business, that does NOT guarantee that you can just go ahead and start. Many cities and counties may let a previous owner "slide by" or "grandfather" them in to NEW codes, but they probably won't let the new owner do the same. If codes or zoning have changed since the previous owner started their business, you will need to bring the building into compliance before you can legally operate there.
Therefore, a really good idea is to ask the landlord or building owner if the building is up to code BEFORE you sign any lease. It's never a bad idea to ask the landlord if they are willing to bring the building up to code or at least split the costs, but even if they decline, at least you know up front so you can plan rather than being surprised after the fact.
Definitely make sure your building is up to code before you start operating.