noun
tipster; tout
A person who sells predictions or tips, most commonly associated with horse racing, but also used for other gambling or speculative contexts.
競馬場の近くに予想屋が店を構えている。
A tipster has set up shop near the racetrack.
彼は予想屋から買った情報で馬券を買った。
He bought a betting ticket based on information he got from a tipster.