Legal, Legal, Legal....
Most states have specific rules for commercial including requiring additional licenses, bond, and insurance. Most have specific definitions for commercial and what a resi license will and wont cover.
Oregon for instance:
Residential GC license allows commercial work on 'small commercial structure'. That means 10,000sf or less and not more than 20ft high, some specific leased areas, or construction projects under $250,000 for all contruction work done on the on structure.  Not your contract, the entire project(including your part) has to under $250k. Link
Anything outside of this requires a commercial endorsement. Commercial endorsement requires a separate bond and much higher insurance coverage.

Electrical licensing also varies. You many be fine running low-voltage speaker cables without a license in residential, but commercial typically requires that any techs running cables carry some form electrical licensing.

Keep in mind that some commercial clients may have licensing, insurance, or safety requirements above and beyond the legal minimums.  This also goes for landlords.  The tenant may want to hire you, but the landlord(who owns the building) may require that you carry certain insurance, licensing, or follow specific safety protocols.  Always best to get TI work signed off on by the landlord or representative before starting work.

Be prepared to get more safety gear.  Most commercial sites(even small ones) require hard hats, steel toes, and pants to be onsite(even for meetings or walk-throughs).  Most also require eye and ear protection when on the site.  A good plan is to make sure you have a full set of all potentially required safety gear for each of your techs.  Also make sure you have your required first-aid kits, fire extinguishers, etc.  OSHA seems to spend a lot more time inspecting commercial jobs than they do on residential.  I think that I have been carded 5 or 6 times in my career and most of those were on commercial jobs.

Permits and inspections are a way of life.  Don't shortcut or assume anything.  Cover your own butt and make sure you have all permits before starting work.  Even on remodel.  Don't rely on the GC to do it.  If they tell you they pulled the permits, do a site inspection before beginning work and collect/sign the permits then.  Rule of thumb, if a wire gets run inside a wall for any distance(other than an existing raceway) you will need to pull a permit and have it inspected.  Be prepared with proper wire types and ratings.  Even a simple speaker wire in remodel needs to be permitted, of the right designation, and inspected.  Once again, slop that you got away with on residential won't fly on commercial.  Commercial buildings, especially leased TI spaces, may have tenants moving in and out a lot.  This means lots of remodels and trades having work done and inspected.  Eventually, an inspector will ask about all those low-voltage cables....  Don't be that guy that gets busted doing work without a permit.  Make sure you have budgeted time for inspections and waiting around for the inspector.  Some of these are worse than DirecTV....

Take the time to learn your local rules and regs and be prepared to bill for dealing with these things.  A simple 4 hour installation may have an additional 4 hours of dealing with permits, inspectors, landlords, and other legal issues.