New to commercial real estate and evaluating lease

I am evaluating several deals where the seller own the property, but without commercial real estate experience, I am having a hard time checking if the seller will give me an outrageous deal on lease. What is the best cost-effective way to gut check if the $ per sqft/year is reasonable? Do I hire a commercial real estate broker? For example, the seller wants to charge $26/sqft/yr for a 2200 sqft warehouse. I am seeing that on the same street 2 mins away, the lease rate for a 22,500 sqft industrial building is $14/SF/yr. This is a big difference, but also a big difference in sqft. In other areas of the city, I am seeing $20-35/sqft/yr for 1500 sqft warehouse.