I think people are having an issue reading the last couple of pages. Froggy isn’t evil and isn’t scheming (technically).
MC’s fief is close to the mountains. If he takes them into his territory, he would gain a ton of income from mining the mountains, which no one has apparently done yet because of the monsters living there. (I believe this is where the MC fought the dragon.) This issue of the monsters is why Frog-Dude asked about the MC’s strength earlier in the chapter. However, the problem is that the fief and mountains are pretty close to the Beast King’s territory and the king might expand his kingdom to include them eventually.
Froggy is playing the long game by forming a relationship with the MC early in case the MC ends up expanding the fief into the mountains, that way he can grow his income with the MC. However, there is a high chance that the MC and the Beast King might get into a conflict over the mountain territories and mines in the future, hence the “Some simple man happy with his tiny village could never pose a threat” and the “I can’t imagine he’ll want to start trouble saddled with those kids” lines.
Probably the only lines worth being concerned about are the “Thank God for guileless [meaning “innocent”] customers!” and “He didn’t suspect a thing” parts, which when you think about them from a merchant standpoint make sense. The MC was a good customer who probably didn’t try to haggle to death or raise the prices on the items he sold to a ridiculous amount. Also if you think about it, Froggy got a deal via a discount on those extremely valuable materials by getting rid some essentially dead weight he likely highly regretted taking on. That was probably better than he could have asked for. And MC didn’t at all suspect why our frog friend came all that way to sell his merchandise to some tiny, practically zero population town in the middle of nowhere with no apparent promise. If our MC was smarter and realized the value Frog-buddy saw in their relationship, he could have probably been legitimate in hiking his prices for materials and had a more even 50/50 deal. So, Frog-Guy is just happy he kept the upper hand and acquired an easy customer to work with.
Long story short: Frogman is truly neutral. Just a merchant who got what he wanted and thensome with only profit to gain for it. You’re free to like him.
At least, this is how I read it. I’m not opposed to learning I’m wrong.