Yeah, it's gonna be hard for them not to add it as some kind of currency or compare the cost to the currency available in the other world. As the author themselves would be Japanese, it would be easier for them to have it as a marketable currency.
One in a hundred isekai author at least hasn't totally given up on worldbuilding and will make it so that the isekaied MC notices 1 copper coin equals ~100 yen. One silver coin is 10 copper coins, etc. Regardless of if those copper/silver/gold coins have any currency names. That sort of system. It's naturally exceedingly convenient for the Japanese readers, but I have zero problems with it. That system satisfies my eye.
Of course there some even more idiotic, fortunately rare, systems in isekai as well, like the country having a yen-equivalent currency, but still all the coins are those normal copper, silver, gold. The merchant tells the MC this costs 2000 definitely-not-yen, and the MC has learned that's 20 copper coins. In other words, that definitely-not-yen currency is just up there in the air, while people still use the standard fantasy currencies. In the worst cases, the author even keeps forgotting that stupid pseudo currency and just talks about silver and gold coins. In this series the currency looks suspiciously like a modern fiat one, but who knows.
But what I found refreshing here was that despite this other world also having an Adventuring Guild of some sort, Ranks weren't divided by Strength but by Trust (and while it wasn't explicitly disclosed, I believe Reliability as well)
Aye, that was pretty nice. Although strength obviously plays a role here as well if you have to sometimes prove it to get rank ups.