Not all tack errors are created equal. Some do matter. In fact, some matter a lot.
There are two major types of errors that can--and should--knock an entry right out of the ribbons. These are: tack that is nonfunctional due to serious fitting or construction issues and performance entries that include prohibited items.
In the real world, the most regulated piece of tack is the bit. Many associations have very specific rules regarding the size and shape of both the bit's shanks and mouthpiece. Exhibitors may even be asked to unbridle their horses for a ringside bit check.
In this respect, model horse showers have it a lot easier. Our bits don't usually have mouthpieces, and even the most thorough judge is not going to whip out a ruler and measure the shanks.
Still, there are a lot of ways to go wrong. On the functional side of the equation, the bit must be positioned correctly at the corner of the horse's mouth. Also, if it's a curb bit, you've got to get the curb chain/strap in the right place.
A missing or improperly placed curb strap is a major error. A curb bit must have one in order to function properly. Depending on specific event rules, this may or may not be a disqualifying offense. Under no circumstances, however, is it a good choice.
Here's why--I photographed this cute pony at a schooling show where the only rules were that tack be safe and non-abusive.
While he was not disqualified for that missing curb strap, there's no doubt that it adversely affected his performance. This was a nice pony with a good riding child, but they struggled throughout the day. I'm betting a lot of their problems could have been fixed with the right equipment.
Other examples of errors that affect the function of the tack include girths that are so loose they don't touch the horse's belly and saddles that are so large they extend over the point of the model's hip.
Onto the second category of tack errors--the prohibited items!
Once again, bits lead the way. The bit needs to be appropriate for the type and level of competition. When in doubt, check a rulebook. Using a prohibited type of bit is a disqualifying offense.
Breastplates and breastcollars are legal--although not always fashionable--for all types of equine competition. Martingales, tie downs and leg protection vary from discipline to discipline. If in doubt, check the rulebook. If you're still in doubt, it's probably safer to leave it off!
Another option is to specify that your entry is competing in an open or schooling show. These types of events are often used as a "get out of jail free" card because of their less restrictive rules. That's ok but honestly, I'd rather see a Quarter Horse showing under AQHA rules. Still, if you really want to show your trail horse in boots, this is the way to go!
Tack is an important part of a performance entry, and no one loves beautifully made, in-scale tack more than me. Still, it's important to remember that tack doesn't have to be fancy, trendy or covered in bling. It needs to be safe, functional and legal. That's it.