What are some ethical dilemmas in selling organs and organ donations?

To me this subject is very interesting coming in the wake of dealing with this with my father in law. There was nothing in his file about what his wishes were if he ever passed away so my mother in law who he is/was legally married to at his time of death had to make the decision to donate his organs. Some people may think that it is unethical to donate the organs of those that do not wish it or don’t have it in their will to donate but in my opinion I think in the time of shock to the family over something happening too fast they make on the spot decisions to do so.
There have been times where I have seen on the news about people selling organs on the black market to those that can afford it and leave those that are poor or in poverty to miss out. Selling organs for profit is very unethical.
There have also been times where I have gone into a grocery store or the gas stations and seen coffee cans with someone picture and a story about them on why they are asking for donations, the one that is up at my local gas station right now is for a 4 month old little girl who needs not only a heart transplant but a kidney donation. This 4 year old was apparently born with a hole in her heart and only one kidney that is only working at 30% as the sign says. This is another way families try to get money to help those that are in need of transplants but are not financially able to afford the cost of the transplants.