What is the difference between the bridal sashes/belts they sell at bridal shops vs etsy?

There's very little difference between the quality of them, bridal shops mark up the prices to increase their profit since they're paying utilities, storefront rent, wages, etc. whereas Etsy stores typically make their own products from scratch at home so they don't have the same expenses to cover. You can always ask Etsy sellers how they're attached to the belts and see the reviews from previous customers.

Bridal shops mark up their prices and I guess in some cases are better quality. However it’s not always the case. I ordered my necklace from my bridal shop and was not impressed with the quality especially for the price I paid. I wish I would have gotten something on Etsy or amazon instead. I bought my belt from amazon for like $20 and I LOVED it.

Etsy seller here.

So Etsy itself isn't a retailer, per se... you're buying from someone who runs their own business and uses Etsy as an online storefront, so every Etsy shop will be different in quality, price, and customer service. If you purchase from an Etsy seller, you're likely supporting a small business and that's fabulous. But look at the reviews and the shop policies regarding returns & exchanges, and don't be afraid to ask message the seller and ask questions! I both sell and buy on Etsy, and have had varying experiences with other shop owners and the quality of their product. I've generally been able to return/exchange items that weren't quite right for me.