In a patent infringement suite it is up to the person doing the violating to show he made a good faith effort not to infringe on the patent. That usually takes the form of getting a written opinion and analysis from a patent attorney that the attorney does not believe there is any infringement, or that he believes the patent is invalid. The wise violator gets this done before he starts making and selling his widget. Failure to show such a good faith effort will often result in tripled penalties. For that reason, anyone looking to copy something or come close to doing so has to look up the patent themselves and pay to get such an opinion or they put themselves at financial risk.
Sometimes that all gets ignored. It costs about $20K just to start an infringement suit, typically. There are no such things as patent police. Many small time patent holders don't make enough money on their gadget to make it worthwhile to file suit. One thing the patent still does for them is guarantee some bigger outfit can't patent their idea and then turn around and stop the inventor from making his own device. The other, if he's really lucky, is a big company steals the idea and makes millions, at which point a litigating group of patent attorneys will usually take the case on a contingency basis. I believe that's what happened when Detroit stuck it to the independent inventors of the cruise control and of the automatic windshield wiper. It took about 20 years, but it worked out for the inventors. It serves as a warning, though to anyone figuring to invent something useful for automobiles, though, that it won't go smoothly even if it is adopted.