1. Straight legged tents are more stable. You don't want your tent to have any excuse to tip over. Tent weights are another big part of that. Remember tent weights, that will come up again later.
2. Straight legged tents have a true 10' x 10' footprint. That gives you a better idea of the space available to you. You want everything to fit within your space. If you have to walk around the outside of your tent to get from your sitting spot to help a customer or leave your tent to walk around, you need to change your layout. Remember it's important to be courteous to your crafting neighbors as well. You don't need to be tripping over each other to get around your set up. It's an invasion of personal space and reflects an unprofessional attitude.
3. That true 10' x 10' footprint also provides the most shade for you and your customers. It also looks more professional and inviting.
As soon as you have your tent up, you want to weight it down. Tent weights are a MUST. The last thing you need is a runaway tent causing chaos. Many companies sell sandbag attachments for tents, but, if your like me, you really don't want to hand over any more money to them. There are plenty of ways to make your own tent weights. A quick Google search will provide loads of ideas. In my case, I used a quick and dirty method. My tent weights are simply milk jugs filled with sand and sealed with duct tape. They may not look pretty, but they work. Besides, whose going to looking at your tent weights when they're so busy perusing your lovely wares? Just make sure you have about 20 lbs for each leg.