I think the difference between a lot of yes- no here is where they a shopping.
Those shopping in cabbage and roses, Margaret Howell, studio nicholson- those are premium brands, and priced so. Those items will more than likely have individual measurements listed, or they will be cut to the brands standard sizes, but quality control will be tightly followed and the clothes will fit that standard. Fabric will be of a certain quality. You can expect that if you buy a certain item, it will look like the pictures, of which multiple are shown. I understand it would also be a costly exercise to try on 4 coats, if each coat is in the £4-500 range.
For lots of us who do return lots of things, we're not buying from those stores, we are buying from the high street. For cost reasons, and maybe for fashion reasons. They don't put quality control in to the same amount. Sizes differ between garments, definitely within styles, but also sometimes within the same style. Cuts can be badly made, shown in a certain way on a model to disguise potential issues, sometimes not on a model at all and expected to extrapolate from a flat lay or hanging shot. Materials are different- if you're not paying for natural materials, polyester types can go from feeling lovely and silky, to feeling rough and cheap, you can't tell.
I went into h&m yesterday. There is a pair of jeans, slightly cropped, that I have in 2 colours and wear a lot in spring/ summer. They have a darker pair out, but I want a longer length pair in the same cut. Well, luckily, these jeans have no quality control, so the jeans in the same size on the shelf, in the same size (regular length) had about an inch and a half discrepancy in length between various pairs. I picked the pair that was longest.
Payment wise, if I was trying on coats, they would likely be under the £150 range. I would either put them on the credit card or use Klarna, and I would expect to keep 1. I would pay the minimum payment on any bills that came in during the decision process, and pay in full at the point of sending others back and deciding on one.