@vasil94 What you say is of course true, but it's not relevant to this particular issue. Reifold wouldn't expect Yuusuke to trust him in the first place, considering their history and how much Yuusuke already knows of his personality. There's no doubt Reifold himself knows very well his own character, and thus knows he wouldn't even trust himself if he was another person meeting himself. His only concern was to fulfill the king's order. Only that. It didn't particularly matter what Yuusuke would think of him. What he faced was a situation where Yuusuke was more likely to leave than remain, meaning not acting as the king wished. In my impression the mind affecting magic's effect is subtle, so it would need to be used early to have a good effect, not late. If he hadn't used it early, it would probably have been pointless to use it at all. However, given his dubious personality and how only a fool would trust him (which he knows himself), he probably didn't think he could convince Yuusuke traditionally.
In short, in Reifold's opinion the chances of succeeding using it were higher than when not using it. Success was all that mattered. However, it only means he doesn't quite know Yuusuke's personality. But for a pathologically lying double agent it might already be difficult to think someone as powerful as Yuusuke is a soft, naive, goody two-shoes, who can easily be convinced to do "the right thing".