I think most likely Maxis will patch in door locks soon. I just opened a bakery that also sells decorated Easter eggs and a few paintings. The cupcake machine is on the back patio, and there's a separate enclosed kitchen area on one side with oven and fridge, with a couch and book nook for my own Sims to use. The rest of the store to the front is all display cases for baked goods with two tables and chairs where customers sit, chat, and eat free samples.
I had my Sim bake everything the night before and put them for sale in the refrigerated display cases. Next morning she opened the store at 9:00am. Since she didn't have to bake, she was able to spend all her time out front chatting with customers. Her boyfriend was also there to help ring up sales. As long as at least one of my Sims was out front helping customers, no one even entered the kitchen area. They all stayed out front. Darn if her boyfriend didn't get abducted though, when they got home that night, so now he's expecting! Oh well...she'll have to hire someone else to help out at the bakery now. :p
