In California is buyer under any obligation to sign a affiliated business arrangement disclosure agreement?

You are not required to sign any contract. However, the seller may require it in order to proceed with the deal. The affiliated business arrangement is merely a disclosure. If you are uncomforatble with the arrangement, then yyou should ask to change service provides. For instance, if the seller's broker is affiliated with the escrow company, you can request to use a different escrow service provider.