An agency contract decides how much you keep, how long you are tied in and how you get out. Read every line and ask about anything unclear.
How long it lasts and whether it renews on its own. Short terms with a clear notice period give you room to leave if it is not working.
The exact percentage, what it is calculated on, and when you get paid. It should be a number, not a range.
How to end it, how much notice you give and whether there are fees for leaving. Large exit penalties are a red flag.
Who decides what gets posted and sent. You should approve anything that goes out under your name.
Your login and payout account should stay yours. The contract should not let anyone lock you out.
A short review by a lawyer costs far less than a bad contract. This page is general information, not legal advice.
QUESTIONS
Long is not the problem. Unclear money, auto renewal and big exit fees are. Make sure each of those is spelled out.
That depends on your contract. Check the notice period and any exit fees before you sign.