Etsy is, in my experience, perfectly safe to use. It is well-known and I have always received amazing customer service from the sellers. You can use your Paypal account there, which I prefer to do as it’s a little safer. I have heard from other people that items come very late on occasion or that their seller was uncooperative, but that is why each shop has a rating system (similar to Ebay’s) where customers can rate the seller based on their purchase and any customer service they received. Most sellers will communicate with you and will be very cooperative if you have any concerns, but just like any site with individual sellers, there are some bad apples. Just make sure to use your best judgment before ordering from a store. If the store has several negative ratings and looks questionable, it probably is. In particular, be wary of sellers from Hong Kong. Some of these stores are okay, but I wouldn’t recommend ordering from one if it seems off. Also, make sure to read the seller’s policies as some do not accept returns. This doesn’t mean the store is unsafe to order from, just that if you’re on the fence about ordering an item, you might not be able to return it. As a whole, though, Etsy is a reputable site that is perfectly safe to use. I have made several great purchases there, as have people I know, and I highly recommend it!
I don’t know much about AliExpress, though. Hope someone else here does!