Old thread, but the simple answer to Audren's problem is that Sofia was being disagreeable because she dislikes children. Sims who dislike children have a negative response to most interactions until you get to be friends with them. However, she should still be able to sell you things as a consignment worker. That's different.
Sofia actually can be befriended if you go straight to romantic interactions and compliment her personality/appearance. She's a snob, so compliments win her over! The normal "Chat" interaction works with sims who dislike children too.