If you are at a venue that is worth your while (enough sales) you will be too busy to be doing anything but selling and taking orders. If you have another person with you to sell your items then making them at the sales point may work but then you have doubled your sales staff.
One problem one may have, is finding a way to display all the items they make. I usually display about 100 different items at a show. I have made some, collapsible, book shelf looking, displays that work well. In only approximately a ten foot by ten foot space it takes some planning to display that many items. I have seen vendors that make some very very nice items, like crosses, but they just have 3-4 different styles so display space is not such an issue for them. If a buyer does not want their one item ,a cross, they just walk on by. I know I outsell most of the other vendors at the sales I attend and still cannot sell as fast as I can produce between shows.