To touch on what jrs.landscaping said, you need to know the laws, that under the table guy gets hurt and doesn't have workmanship comp you can very easily get ******. When you brake laws such as tax evasion you open your self up, you will have no protection if an injured employee brings suit against you. Insurance won't cover it, being an llc or corp won't protect you from losing your house even your wife's savings. Here's what is often a problem other people have, fire that under the table employee because he sucks at his job or even steals from you. If he tries to file unemployment then the state will find out you are hiring illegally. Many states will come in and hit you with still penalties, which are usually high enough to drain a small/medium landscapers saving causing them to sell off their equipment, truck, trailer to pay it.
Why do people not respect us as they do other tradesmen? Because every Tom, Dick, and Harry doesn't think he can be a plumber or electrician!