I know Kara of A Cake to Remember has written a post on this, but I wanted to do a quick post on my own little twist to things....
I hear some of the strangest things from potential customers. I have had someone concerned about the "red" in the red velvet leaking through the buttercream/fondant. I have heard that you must use pound cakes to stack cakes so it can support the weight of the cake above it. I have heard that you can never pipe black on white buttercream for it will run. I have heard "I was told that I can't do XYZ." I don't exactly know where they get some of these things, but I can only assume another "caker" told them this or it truly is a concern that they fear might happen.
I would like to address the second one first, and say that if you have a concern, just ask. We realize that everyone is not a cake expert, and most of us will be happy to explain something to you.
As for the first one where another "caker" told them so... I always wonder if that other caker really told them that or if it got lost in translation. I don't know how many times people talk about layers when they are really talking about tiers, so it seems logical that folks may be told one thing, but hear it another way.
Of course, they could have spoken to an inexperienced caker or employee as well, or a less experienced caker in the area of concern (I have not done every single technique in various combinations of colors, mediums, etc. and I don't think anyone has). With me, I have no problem telling folks that I haven't done XYZ before... I am sure that scares some potential customers away, and that's fine, but I would rather say that then make up some answer that may come back and bite me in the butt.
There is also the chance that something really can't be done. One of the things that comes to mind is many of the "ruffle" cakes out there. Some of those just can't be replicated with just buttercream.
The final possibility I have thought of is the customer's vision versus the caker's vision. A few months ago I had an inquiry for an Effiel tower cake, and immediately I start thinking of a multiple tiers, stacked and iced together, with a lot of small strips of gumpaste and a ton of detailed pictures to look at as reference. Basically my brain goes here or here or somewhere in between. I give them a large quote, and of course, did not get the order. I can only think about what that potential customer might have said to another caker, "So and so said it can't be done under a million dollars (no that wasn't the actual quote)." In reality, the customer may have been happy with something more like this (This cake was made by a mom for her daughter... she did a great job as a mom who challenged herself by doing this. I am NOT making fun of this cake.), but it was not my vision when I was quoting the customer.
I also had several other instances where folks sent me a cake that fed 80 or 100 and wanted to scale the tiers down to feed 20 or 30, without losing tiers or having a ton of leftover cake. Again in my head, I couldn't scale down a 3-tier cake to feed 15 or 20 and still get the same effect or have a similar quality to the picture they sent me. I just don't think there is enough room to sculpt a baby's butt and legs out of cake and put it on a 6" round cake and have it look good.
So the point of this post? Ask questions, ask for suggestions, ask for an example, etc. It's good for all parties to be on the same page.