Can you get banned for boosting in League of Legends?

The short answer is yes but very unlikely.

Riot Games themselves have stated that only second time offenders will be subject to a ban for MMR boosting in League of Legends. On top of that, it is extremely difficult to distinguish players that are playing with friends from players who are paying someone to play with. That is why duo boosting orders are incredibly difficult to detect of boosting and are unlikely to be affected by boosting bans.

For solo orders it is a bit more obvious when the accounts are boosted so they pose a higher risk of getting caught. Although, the risk is still very low and first-time offenders are not punished severely.

Typically, boosting providers such as Eloking take various steps to reduce even the slightest chance of the bans happening. That includes playing only from high quality accounts for duo orders, VPN usage for solo orders, free spell and champion selection, and much more.