Reasonable Agent Commission

[Khaled Seirafi]

I'm looking to sell a mixed use building, with commercial and residential units, in San Mateo. I'll most likely be working with an agent who specializes in mixed use properties and works for a national firm. What would be a reasonable commission rate?

Also, I'll most likely be using the same firm to buy a replacement property out of state. Can this be a factor to use to negotiate the rate down?