Been cutting for about six years now and lately I've noticed more people burning whole sheets on files that were clearly generated and never actually tested. So here's what I check before I hit go on anything I downloaded.
Zoom way in on the cut lines first. Real files designed for laser work have closed paths and lines that actually connect. AI stuff tends to have gaps, doubled lines, or shapes that overlap in ways that will scorch the heck out of your material. Then look at the details. If a design has intricate lacework where some bars are hairline thin and others are chunky for no reason, that's a red flag. Thin sections that fine will just char or fall apart.
Also do a quick test cut on scrap, always. Even a legit-looking file can have line widths set for a diferent machine than yours. A two-minute test on cardboard offcut has saved me more full sheets than I can count.
If the file comes with no info about material thickness or settings, that usally tells you the person never cut it themselves. Skip those and stick to designers who post their own results.