Winner

Alex didn't need the Pill testers, but he still brought out 5 of them for everyone else's sake.

"Please give me your pills," Alex said to the first man to his left. While he looked through the pills and put them one by one in the 5 different testers.

As they waited for the result to come, Alex asked the man, "What did you think of the recipe I gave you?" 

"It was good," the man said with no other expression on his face. Alex immediately knew he hadn't used it.

The results came and the best pill was around 56%.

Alex went on to the next one and did the same thing. This person said that he did use the recipe, but only for the last one, but it was the first time he used that recipe so he got a little confused and messed up.

The results came and his best pill was around 53%.