If third-party services guarantee the stream then one must not rely on it. It is because these are not legitimate. 3rd party violates the terms and services of Spotify. Any service that claims to offer placement on the playlist in exchange for money is considered to be violating terms and conditions.
One must not use a third party and must not accept the offers. If someone accepts the offer may have to bear negative consequences. The team may take action like withholding royalties, correcting a number of streaming, and measure the song and artist's popularity. Spotify has the right to cancel the manipulated content from the playlist.