In this Mishnah, we'll talk about those individuals who are mumchin (experts). They were experts in checking the blemishes. Were they allowed to take payment for their work? The Mishnah says: If somebody takes payment to check the Bechorot (firstborn animals), you're not allowed to slaughter based on his testimony. We're concerned that he may permit the slaughter because of the money he's going to receive, which would be against the Halakha (Jewish law). Even if this person is known to be an expert, we say that the idea of him taking money could possibly sway his decision-making. The exception was an expert like Ila, who lived in Yavneh and was a very pious individual. There would never be any suspicion that he had a bias toward permitting the slaughter. Therefore, he was allowed to collect payment for checking the mumim (blemishes).
The rabbis allowed him to take four issar (ancient coins) for examining a small animal, like a sheep or goat, and six issar for examining a large animal. A large animal was a lot more work. There was more involved than checking the blemishes. Greater effort had to be put into getting the animal onto the ground, tying it up, and then checking the blemishes. The smaller ones were not as much work. Therefore, he got paid more for inspecting the larger animals. He was paid for examining the Bechorot, whether the animal was unblemished and was not allowed to be slaughtered, or whether it was blemished and permitted to be slaughtered. He had to take payment no matter what. If he only took payment when he permitted the Bechorot, people would have suspected that he was allowing it only to get paid, even though that would not have been true, because he was a very pious individual. But he was given the money no matter what. Therefore, there was no reason to suspect him.
The Chachamim (rabbis), who were not on the level of Ila, were not allowed to take money, no matter what the situation was—even if they took money regardless of their judgment, and even if the Bechorot was found to have a permanent blemish. They were concerned that perhaps they would be lenient in their decisions so that people would come to them, and that they would be known as the rabbi who permitted it, the mumcheh (expert) who permitted it, so people would come to them. Only someone like Ila, who had that super piety, was allowed to take money, but he had to take it regardless of what his bottom line would have been.