The actual definitions are:
According to Oxford Dictionaries
2 INFORMAL : Cheap, unpleasant, or blatantly inauthentic
a big cheesy grin cheesy motel rooms
I do not want Cordelia getting emotional reassurance from a cheesy, cheap, plastic phone.
I've seen people invest hundreds of dollars on a state-of-the-art graphics board, and then connect a cheap and cheesy monitor to their
And that's not to mention the even more lucrative video market - the natural home for such cheap, and unashamedly cheesy, comedies.
According to Oxford Dictionaries:
2 INFORMAL : Arousing feelings of doubt or suspicion
I’m convinced there is something fishy going on
That doesn't mean, of course, that you should give the next wonderful scientific speaker you hear a fishy glance of suspicion.
He comes home too late, he gives fishy excuses, a strange woman called the other night and hung up when Patty picked up the extension.
Some of its doctors were implicated in the murder of their staff members who had suspected something fishy about the whole thing.
So, to answer your question, "fishy" can be considered a synonym of fraud, but I wouldn't say so for "cheesy" (not conventionally, at least). However, since both words have an informal usage, you could expect to seem them used interchangeably in some places.