She made great points about the people displaying, but I want to add onto that. When you attend an artisans display at Pennsic (or anywhere else) you should keep in mind that those presenting are likely to be a variety of levels in terms of skill. Some might be new to the SCA and are jumping into the deep end and displaying during their very first year. Some might be veterans who are exploring a new art. And, most importantly, some might actually be displaying something entirely other than what you think you see.
Usually the first two categories will become apparent once you engage with the artisan and you can handle advice accordingly. That last category though, can be tricky, but you should always ask yourself - and the artisan, if necessary - what it is they are showing. I can use myself as an example, I study Viking Age Norse textiles. I have a nice display of wool, textile tools, a small scale loom and books that house my research. What I was NOT actually displaying was my woodworking skills on the loom that I made for the display. What I was NOT displaying was woodwork or pottery for my spindles (which I did not make at all). I was also not displaying weaving or spinning (though I had woven samples and spun wool there as well). What I was sharing was my knowledge of Norse textiles, how they were made, and also the context in which they existed in period. I know that people do not take time to read piles of papers at events, so I illustrated every item with something tangible on the table. (Realistically, you could say Research, and Illustrated Research, as well as Experimental Archaeology, are my actual A&S "things" in the SCA, not weaving or costuming or any of the other things I do. My geek is in the research and experimenting with what I learn.)
I also have a couple of friends who make and display textiles tools. These people are, in fact, geeked up over making period tools, though they may or may not actually be interested in spinning and weaving full lengths of cloth for garments. This is actually a very period practice (especially as you get into later history where there was a greater division of labor and people were more apt to specialize, meaning that a Renaissance era woman would labor to spin fibre, but would be procuring her spinning wheel from an adept craftsman who specialized in that trade). If someone builds a loom and displays it, it is fine to ask if they have woven the cloth for a garment on it, but it is also fine if they say they tested it to see if it works, but they have little interest in weaving 5 yards of cloth.
If you are attending a display, please keep in mind that what you see in front of you might not be what it seems on the surface. Remember that just because you prefer to do things from sheep-to-shawl (including making all of your own tools), please remember that not everyone has an interest in doing every tangental aspect of their craft themselves (and it might not be period for them to do so). This is NOT a competition where you get more points for each item one fashions by hand. You will learn more about someone and their art if you are willing to walk away from assumptions that you might initially make when you learn that those assumptions were off base.
And please, please, remember that many people love the research aspect more than any other and their displayed craft might just be to test theories, it might just be to help illustrate the folder of papers sitting in front of them. If you are interested enough in their work to stop and talk to them, you should be interested enough to accept that they might be more interested in sharing their research with you rather than the fine details of a machine sewn costume that is only there to help people visualize a paper they composed.
And for the artisans, I recommend that if you make modern substitutions (let us say buttons for your costume), but you have no interest in metal casting to make your own, that you still learn (and include in your documentation if it is a competition) the historic source of the buttons. Would they have been locally crafted or imported? Was there a guild for this? Were they expensive? (This type of knowledge can also help you better place your garment into historic context.)
I look forward to seeing this year's display. It is an amazing day of geeking out with others and learning from them!