... or anyone really. Many people don't realize that praise is a subtle form of judgment, (favorable judgment usually, but judgment nonetheless), accompanied by the implication that one is qualified and called to do so.
One of the things that mystics go through as they move through their own set of lessons is to learn to manage ego... identify it, its methods and results, get leverage on and control the thing until it ceases to operate, or operates within parameters such that it creates minimal distraction. There is a middle stage where this seems the most difficult.
Digression/ I vaguely recall reading somewhere decades ago of a mystic-type, possibly sufi, who would suffer all sorts of questions, doubts, even bad behavior; but if you praised him directly you would be instantly on the receiving end of a torrent of invective, as well as a soundly swung cane, if only within reach. The person bearing the praise was seen to be a demon trying to fan the flames of 'ego' into life through a back-door sort of method (the favored door of ego, often). And so the mystic, trying to preserve his hard-won freedom, was fierce in his resistance. /Digression
This middle stage consists of having some model of the problem, but as yet little or no model to remedy it, let alone a practical agency.
It is especially difficult in the presence of other people. There is a reason for (the quintessential) retreating to some mountain cave for a long period: Ego (for us humans, at least), is largely a socially derived phenomena. Think about it: Suppose you were going to spend the next 1,000 years alone doing research on Planet Zorptron. No contact with anyone else, with the possibility of there never being any ever again. Concern with hairstyle, cut of suit, the statement that your handbag makes, or the style of vehicle you may toot around in fades into utter insignificance. You would also develop a friendly, easy, yet impersonal relationship with your modelling system (uterus in which ego can take root), which in turn no longer has to spend most of its resources modeling YOU. And also, no one would be collapsing your waves to fit their belief / modeling systems. Nor would you be compelled to distort your own consciousness to fend off this common intrusion.
Even once a mystic gets past that stage, and has no more trouble with ego than with any other form of flatulence, direct praise still doesn't do; Although they can then easily suffer that form of behavior as well as they can other less-than-drawing irruptions of yet-to-be-trained children. But they don't relish it.
If you want to 'praise a mystic' or show appreciation, the best thing is to, well, not want to; but else wise, show respect for his or her ideas by vetting them and asking, perhaps, questions as you might want, to clear things up, or even better, bring something to the table (not already there) that compliments the ideas or even reveals a new dimension or depth that was not there previously, or even better, put those ideas into use, visibly so, or even otherwise.
... or simply do nothing at all, but just be part of the flow .... building bridges, planting flowers, singing songs, dancing the dance.
(Sorry for the preachy tone.)