I have an Etsy shop. Unfortunately Etsy has something called 'Etsy labels' which they advertise for use by sellers. These postage labels give an estimated delivery time.
I refuse to use them for my parcels as, when it's busy, like Christmas, or if Covid has hit a delivery office it gives a very false sense of delivery times. Customers get, rightly, edgy and sellers get inundated with enquiries when it's just volumes in the postal systems. I tell my UK customers that I use first class post so they know how long they would usually wait and, at busy times, they give it a bit longer before they worry. By which time the parcel has edged through the system.
Did the seller tell you how they'd sent it? Sometimes, if it's not on their dispatch note, it can be shown on their shop. If it's by second class post that could show why it's taking so long to arrive. If they didn't mention how it was sent, many sellers add the information on their individual items pages - usually just down from the price. It'll say delivery estimated by (or something like that) and then may have some information about which postal service they use.
Or it could be on the seller's main shop front page, scroll down to the information about the shop. There may be a FAQ about delivery which will include how they ship .
As well as selling I've also bought from Etsy sellers a lot (I buy some of my supplies from a few of them) and I've never had a problem. Like most platforms, there will always be people who scam. But most Etsy sellers are small businesses like mine who really value our customers.
As others have said, join as a customer and if you can't contact the seller, contact Etsy direct. They'll help you.
Good luck!