I'm trying to understand the 「まいとしているふうなのだ」 part in:
さっさと言われた通りにすれば良いものを、店番の男はなぜだか渋面をして相手の要求を頑なに聞き入れまいとしているふうなのだ
As far as I can understand:
さっさと言われた通りにすれば良いものを: Although he should quickly have done as told
店番の男はなぜだか渋面をして相手の要求を頑なに: the clerk for some reason grimaced and stubbornly
聞き入れまいとしているふうなのだ: "To comply", and I'm not sure what the rest means.
I think 「まい」 means "doesn't intend to" (second meaning); maybe 「としている」 is part of the various meaning of 「とする」, but I can put my finger on which one. Here l'électeur said all of the different meanings of 「とする」 share a meaning of "making a decision of some sort", so maybe 「としている」 shows that the clerk decided to not comply with the request?
As for 「ふう」, is it the same as in 「こんなふう」, meanning "manner"?
If I'm on the right track, the sentences would mean something like "he didn't intend to comply"; still I'm not sure about the interaction between 「まい」 and 「としている」 ("he decided to not intend"? Kinda awkward and wrong-sounding), and about how 「ふう」 fits, I basically ignored it.
As per 「なのだ」, I guess it's 「だ」 > 「な」 copula + explanatory「のだ」.