The only trick I know is locking the house door for visitors. Because it's so damn annoying when I pose Sims for preview pics on a lot I use for this, and the postman stops by, walks around, while I want to take a pic for outfits to preview. Then there's that other NPC bringing a computer as a welcome gift, trying to find somebody to chat with... So for clothing preview pics I still prefer to use Bodyshop, in one click the picture is taken.