Fooling a flimflam is fooling a flimflam
Fooling a flimflam is flimflamming a flimflam
Guster Goosed A Goose With Great Gusto
The first two do not make sense, grammar wise.
Flimflam is a verb that means to swindle, so that looks to be used correctly.
However, the noun form of the word flimflam means a sort of insincere and nonsensical talk. It does not make sense to “fool a flimflam” or “flimflam a flimflam” as a discussion or talk cannot be fooled. It would be better to replace that with another word.
As for the last tongue twister, this is a good one! It is funny and grammatically correct!