She's really corrupt, even by isekai standards, abusing guild authority for personal gain. And over such an odd thing as fruit. Is this stuff narcotic or something?
No? As she stated herself, corruption would be swindling, making unfair claims to diminish others. The only would-be "abuse" here is if her statement wasn't backed by the guild (not handling the mediation in the future), but if you pay attention to the dialogue it's more like a verbal agreement made out a noble's request (a "higher standing"), not a contract written in paper or anything. And she was fairly truthful about that too. It's clear no other buyer seemed interested, there is no mention of the guild getting a commission out of this either, if it was possible at all to lease.
I actually want to take a step back and remind you as well that the noble planned only on renting the land, and if they built a house there, it would be the noble's property after the rent expired (not to mention the noble would also probably increase rent or try to get out of the agreement at that point, which is a scummy practice done IRL at least in my country, so imagine then in a world less advanced with nobility and crude laws).
not to mention, the guild isn't a specialized agency for real state, they are more of an all-rounder institution, therefore it's not unthinkable for them to back promising adventurers who are bringing money and increasing the standing of the institution. The remaining was just her leveraging the information she had to bring the price down and haggling to secure the purchase (which again, wouldn't happen otherwise).
to conclude, the "unfair" points were a potential misuse of the guild for personal purposes, not declaring it as a personal transaction instead of doing so as an employee of the guild and undeniably an obsession over fruit that really can't be explained other than being the equivalent of cigarettes in that world. None of that make her corrupt, although unethical.