Hopefully, the majority of your customers will be lovely. Unfortunately, if you have a booth long enough, you will probably come in contact with some who are morally challenged. There's no sense in getting angry or letting them spoil your day. I always trust that karma would take care of them. You reap what you sow. Etc Etc.
Just as there are things you can do to make your home a less attractive target for a burglar, there are things you can do to make your booth a less attractive target for dishonest customers. Honestly, my suggestions aren't great ones. They are just deterrents. And I would be willing to bet that there are more helpful ideas on this topic. Comments and suggestions are welcome!!!!
It's super easy for someone to come along with their own pen and mark through your price and write in a lower one. One solution - never slash your prices on the original tag. Have a special tag that you ALWAYS use for sales rather than just crossing through a price on the original tag and writing in a new one. Let everyone who works the register know that. Solution is actually not a good word choice. Someone can still mark through it and unless you are working the register, it can still be rung up with the new "thieving customer" price. Lets just say this idea is a decent deterrent.
When I had a booth, I would get calls at least once a month for a price on an item with a missing tag. I knew I was great at putting on tags in such a way that they weren't going to fall off. They were being pulled off deliberately. At first, I would just go to my spreadsheet and look up the price. But then, I got irritated. I'd look on the spreadsheet and then quote a new price that was a little HIGHER than what was on the tag. If they really wanted the item, they might go back to the booth and miraculously FIND the missing tag. Or, they'd pass, leaving the item to be purchased by someone more honest (after I'd made a new tag). Making new tags is irritating. Side note - whenever I rearranged my booth, I'd almost always find a tag on the floor behind and or under things. The hole where the string had been was generally torn.
Another possible help is to use the tags that are hard to pull off. Tags with reinforced holes require a bit more effort. It can still be done, but again, it's a slight deterrent.
I am always amazed at how many vendors don't write enough info on their tags. If you simply write your dealer number and a price without writing what the item is, you are begging for a switch. A customer could grab a $9.99 tag and take it to the register with a $24.99 item.
Be sure the description on the tag is good. One vendor friend had two windows for sale. One window was plain and small. Another was large and special. A customer grabbed the tag from the cheaper plain one and used it to buy the much more expensive one. Both tags said simply "Window".
There's no perfect way to prevent dishonest customers from pulling a fast one.Unfortunately, there are dishonest people out there and this is the kind of thing that you need to figure in when pricing. Big stores know to expect theft and breakage and they price everything a tiny bit higher to offset those losses. Unfortunately, a smart and determined scumbag will probably succeed somewhere in the store. If this is a big problem at your mall, then the mall needs to step up security. Having very visible security cameras is a good step in the right direction. Having enough people working the floors is another.