One of the primary advantages to a corporation is it basically isolates your personal wealth and assets from the business. If someone sues you relating to your business, product or business practices, only the business assets are at risk. (unless there is something more criminal involved in which case civil suits could go after all a persons assets.)
In the case of selling prints or art work, there is little or no risk to your non-business assets. The other big advantage is a corporate structure allows more flexibility in how profit is treated with regards to compensation. Part of any profit can be returned as operating capital, put into an R&D account etc. In some cases you can work it out so as not to make a salary and thus avoid paying employee taxes on yourself. With a sole-proprietorship all net profit (over $400) is subject to self-employment taxes.
As far as sales tax goes, a lot depends on where you live and how you sell your goods. Most small businesses that sell to customers out of state and over the internet do not collect sales tax on those transactions. That is one of the single biggest advantages to internet sales. (although congress and state governments are looking at ways to compel web merchants to collect and return sales taxes). The only thing that worries me about this is that the laws could be changed in the future and the state revenue department come back and require you to pay all the back sales tax that you never collected.