The appropriate convention dress code differs by industry, but business casual is typically the preferred option. Even in industries that are more casual, wearing professional looking clothing can make one stand out and appear more credible. Whether a vendor, attendee or simple visitor, dressing on the nicer end will help you stand out and command the attention of whoever's busy schedule you hope to meet with while at the convention.
Conventions are excellent places to find potential customers, business partners or even new jobs! Because of this, it's important to maintain a professional image and dress the part. Often conventions are in resort destination, so its tempting to dumb-down your clothing and treat it like a vacation, but avoid this while at proper convention functions. Appearing too formal can give others the wrong impression about you and potentially ruin any beneficial relationships.
Wearing a sport coat can really set you apart and get you positive attention in convention settings
If you are an exhibitor, dressing more formal gives you a more credible appearance
Don't dress too casually, or you may not be taken seriously by other vendors