The way I look at it, a customer has a right to hire whomever they want. I wouldn't directly solicit the business of a former employer, but I wouldn't turn down their business if they called me.
In regard to yellow page ads, I think the answer depends entirely on your market area. There is only one directory service in my area and most people consult the yellow pages if they don't personally know an electrician. In the small town where my parents live, most of the contractors do not advertise at all. It makes it extremely difficult to find somebody to do your work when you don't know who to call.
In regards to business organizations, I would highly recommend consulting an accountant (and possibly an attorney) before making that decision. The account can advise you as to the tax liabilities (don't forget state and local taxes!!!), and the attorney can advise you as to legal liability and legal requirements.
Finally, I'm an electrician who also happens to be a commercial property manager. It never hurts to drop your card off at the property manager's office, but remember that most tenants are responsible for their own internal wiring - so don't forget them.
Sure, many businesses are slow paying, but others pay well. You'll just have to do your homework by checking references. Many contractors are major rip-off artists as well. It took me several years as a property manager to locate an HVAC company that wouldn't cheat us at every turn. So, most property managers are just as leary of contractors as contractors are of property managers!
And as far as estimates go, that's just part of doing business. Many times property managers need to know what it will cost to build out a space to tenant's specs in order to calculate a rent rate, only to have the deal fall apart at a later time. I generally tell my contractors how likely I think it is that the deal will go through so that they don't waste too much time on it. Often, I just need a verbal ball-park price for my calculations. The main thing is to try and work with the property manager to establish a mutually beneficial relationship. (Granted, this isn't always possible.)
