Is it a good idea to post your prices or not? i have been contemplating posting to my website and facebook page a serving guide and the associated base price for potential customers to look at and weed out lowballer people wanting cake for $1.50 per serving. But then the prices are out there for competitors to see and such.

Who posts and who does not post prices and what are the pros and cons?

I wouldn't. Have a menu with basic pricing to send to clients who are inquiring seriously. 

I prefer to use a minimum order as opposed to posting pricing..posting price for customers who don't understand how pricing works can backfire they might assume that a carved cake starts at $4.50 a serving etc.. For that reason I prefer having the minimum order that way customers know pricing starts at $150 or $200 or whatever.

I have listed my basic  prices by the size of a cake. People don't read,  they ask anyway.

I offer a wide range of products, so my bakery items all have pricing.  As for cakes, I offer a dessert cake line in a variety of sizes and flavors.  I do show the basic flavor pricing and the add on cost to upgrade to a more expensive flavor or frosting or filling.  I note to prospective clients that I offer event/wedding cakes and those are priced to order.  I think it would depend on what you intend to offer.  

9 times out of 10 they don't usually view the pricing/menu first but I have found that it's very convenient having one available as a way to familiarize them with your pricing especially if you are unavailable to quote them. I have a "basics" price list and note that specialty flavors, fillings and icings increase price as well as the design. I also offer a variety of items and some are seasonal so I don't have a set price on them. Plus with the ever changing costs of fresh fruits it's hard to keep a set price when your small like we are. So I do have it noted that fruit pies vary in price. For us i don't think I could run my business without one posted and readily available :)