The short answer: no.
Whether or not you accept a pitch from a brand is completely up to you. Keep in mind, you can always try negotiating with a brand if you want different terms such as compensation, etc.
If you're receiving pitches that aren't relevant and/or don't include enough compensation, be sure you:
1. Choose the categories (up to 5) that best match your areas of expertise
2. Set your Minimum Accepted Free Product Value and Minimum Accepted Cash Value within the Payment Information section within your account.
If someone pitches you something inappropriate or illegal, please flag the transaction for review.
If you decide to flag a transaction, the process is simple: within the message panel of the appropriate transaction, you can click the menu options icon in the top right corner then in the dropdown, click Flag this Transaction.