What is the most difficult product you ever sold?

Dear [Name], I think Hematology instrument was difficult. Do you know that? Hematology is blood test for Cell counts. For example, Red cell, White cell, Platelet and so on. My company was a distributor of Horiba Medical in Korea. Horiba was not famous in our business. So, we must compete against the high level company. For example Sysmex, Beckman coulter, Abbott... In sales of Hospital, Name value is very important point to choice instrument. so I should have suggested low price than competator. but I took a win in big instrument order against competitor. My boss gave a grate thanks to me. but it was impossible to change ours. After domostration, our instrument did not work nomally. so our company withdrawered our instrument from the hospital. I think, it was very bad remember to me. I apolozy to my customer and our staff. after that time, I resigned that company. I could not sell that instrument to my customer.