I let anyone shop if they ask, but don't usually ask for it myself because the process can take so long (especially in the Ables...) Most people are just looking for a quick trade and that's fine with me, if I really wanted specific clothing I'd just ask for it on here. I do often take the offer of someone says I can do it though.
I never really worried about the custom designs, we have a feedback system that I can use to tell that someone will have good manners or that I can use to warn others if they don't. And even then, I did put up some custom stuff up there myself and I could just replace it
I think most people don't even realise leaving designs is an option though.