The answer to the riddle

It doesn't make sense to add together the money paid out by the men (which is no longer all in the same place) with the money in the clerk's pocket. It's only a coincidence that the sum is close to $30.

The money is accounted for as follows:

The men paid out $30.

They got back $3 in refunds, and $2 went into the clerk's pocket, and $25 is in the hotel's cash register.

3 + 2 + 25 = 30, and nothing's wrong.