As a wedding service provider, this is an important one to be let known. Over the past 19 years, I have been DJing weddings and providing other services such as balloon decor and other entertainment. During this time, I have become aware of a variety of scams, both for the engaged couples and the service providers.
One of the biggest is the fake wedding show. There have been some shows (luckily I have not encountered them personally) which are just outright non-existent. I've heard of couples who bought tickets and vendors who bought booths show up for the event to find the location knows nothing about it. Always check before buying booth space that the venue is actually booked for the occasion...a quick phone call will tell you that.
Another is commonly known as the Dress-Label Scam. There have been cases where bridal shops have changed the tag on the dress to hide important information. They might change a low-grade silk-like material gown's label to say silk to charge more. Some even just change the label to hide it's origin. Maybe it was from the Bargain shop and they want to sell it as a designer gown. Now of course it is really hard to discover some of these, so the best way to protect yourself is to work with reputable companies with good references and Better Business Bureau rates and such.
Getting married abroad can present some problems. Obviously it's harder to check on the qualifications and actual locations if you are not a frequent traveller. Some places will overcharge. Some weddings are not recorded or officiated by unqualified or uncertified persons. Worse of all, check to see which countries wedding licenses/certificates are recognized by your own country.
And now my own personal thorn in my side: Service Providers who let you down. There are some providers who are all- out scammers just out for you cash. Again, check references. Also check licensing. Here's my thorn as a DJ: There are so many unlicensed DJs out there. If you visit AVLA.ca you can learn all about the licensing requirements of DJs. There's just too many out there downloading music, thus having no overhead and charging very little. That is a red flag right there. A friend's brother just had their DJ they hired get fined for copyright violation and not being licensed.
Weddings should be a time of great joy. Relieve undue stress by protecting yourself from these scams.