The more I see online, the more I realize that there are different levels of business people. Some are totally laid back about how they run their business, so for them completing the entire transaction via text or facebook messaging is ok. Others prefer to be a tad more professional and would do things professionally via established business channels like business email or a website contact form. There are different levels of cakers out there with little to no business savvy all the way to hard-core business mavens.
As our world continues to get more social, I think it's important for the business person (us) to do what we can to guide clients to acceptable channels. The last 2 orders I filled started on facebook. I usually have no problem answering general questions on facebook like: Are you available on day x? How many tiers/cupcakes would I need for my baby shower? In those responses I almost always I'll include a link to my site. Once the conversation gets serious and they're talking pricing or quotes I send a link to my pricing page and contact form, and ask the client to fill it out if they plan to order.
There are times when you literally have to 'move' the client from facebook to the business channel. Can't count how many times I've pulled info from a facebook convo, summarized it in an email from by business address so that the client can just hit 'reply' and we go from there. And you'd be surprised how often clients would go right back and respond via facebook LOL.
I think it's about finding balance. If I had been zero-tolerance about any order-related contact via facebook, I may have lost those orders. No matter how a client contacts me, if we have an order, it would have to go through MY established channels even if I have to move the client to that channel.