Mark everything up 500% and tell everybody that all your guns are "Pre-ban" and worth more money. Do not include any magazines with any of your guns as that would be cutting into your profit margin, make sure you sell the magazines seperatly, even if they came with the gun in the first place.
Display the beanie babies at the front of the table. Jewelry at the back. Knitting and artwork on the left, and finally cheap Chinese plastic toys on the right.
Make sure to wear BDU's and camo face paint, and get one of your 350 lb ultra tactical buddies to do the same and hang out with you. When anybody ask you why you are dressed like that, tell them its classified.
If they have questions about your guns, just look at them with a confused face and say very firmly "everything is sold as is, no refunds".
And finally, but not least, make sure to have the chili cheese fries and corn dog mustard spilled all over yours and your 350 lb buddies shirts. This conveys a very professional image.
Hope this helps. Have fun.