"Girls come in and tell all kinds of horror stories," said Mrs Waldron.
"They've bought their dresses in what they thought was their size, and they don't fit properly at all. What they're buying from those sites doesn't match what they see in the photo. It's really disappointing for them. Without trying it on, they're taking a big risk."
Fellow dressmaker Carolyn Henson said business has 'dropped dramatically' for her since girls started buying ball gowns on the internet.
However, the number of clients asking for alterations to their online bargains has skyrocketed.
"I am altering more dresses this year than ever before," said Mrs Henson.
"Those dresses are not made to measure. You send your measurements, and they select something similar to your measurements. So chances are they will need major alterations."
Mrs Henson said she most often has to take in dresses that are 'way too big', putting panels into dresses that are several sizes too small.
However, she said, some dresses simply cannot be altered.
"I had one girl who bought three dresses online to get the right one."
Dress designer Rasha Taylor said she receives 'around five calls a week' from girls that have ended up with 'a glorified rubbish sack' for a ball gown.
She said New Zealand has become a target for international online dress scammers who peddle poorly-made replicas of designer wedding, evening and cocktail dresses using New Zealand domain names.
"Most people think that a site that ends in .com or .co.nz is legit, but that does not mean it is from New Zealand or the US," said Mrs Taylor.
"Countless scam sites disguise themselves as Western businesses." She mentions one 'New Zealand' site which is registered in Hong Kong. "They are an agent that has multiple factories they source gowns from. They are not quality-controlled."
She said one of the biggest problems for New Zealanders buying from offshore sites is they are not covered by the Consumer Guarantees Act, and thus have no rights of return or refund.
Therefore, they undergo the costly process of having their gowns altered - a service Mrs Taylor does not offer. "Many of the online ball dress disasters I have seen would require so much work to fix that the customer is far better off buying a whole new dress," she said.