@pontipinemum - I buy almost everything on eBay or Vinted. I began on eBay & Etsy over 22 years ago, because I loved "proper" vintage clothes & accessories. Now I buy from these sites because I'm less well-off (& even more environmentally aware), so it's more of a necessity - but I still find it fun!
I rarely make mistakes though - & that's mainly because:
- I know my own style;
- I know what brands I like;
- I know what fabrics I like; &
- I know what colours & shapes & patterns suit me.
I also try not to impulse buy, & make sure to ask for measurements, fabric content etc (& check against something I already own that fits well). Vinted in particular encourages you to buy instantaneously in case you "lose out", & there's also the thinking that you can just re-list something that didn't work out. I've done that in the past a few times & regretted it - the secondhand market, especially on Vinted, seems rather saturated these days, & things can be hard to re-sell. It's not a very sustainable approach either, & rather defeats the point of buying used/secondhand/preloved (take your pick!) in the first place.
I also don't buy things just because they're currently in fashion. I buy things that fit with my own style - & some of those also happen to be in fashion, so they help freshen my wardrobe & keep things up-to-date. For instance, I'm avoiding anything polka-dot as they don't suit me - but I love & suit balloon/sarousel trousers.
That's not to say I never hit the Buy It Now button - I do, but only with things I'm certain about (often they'll have suddenly appeared in one of my saved searches). So, for instance, a specific pair of Zadig & Voltaire boots that I'd been after in my size - this took me five years! They were & are classics though, & I love them ... but normally I have just waited a few months or so to get my hands on something I've fallen for in a shop or online.
I could recommend the brands I like - assuming you want the upper end of high street clothes rather than designer? But I think you need to look & try on in various stores to get a feel for what brands you like yourself & which suit your shape, style etc? I like different brands for different things - for instance, Jigsaw is good for coats, bags & boots in particular, & M&S Autograph does good knitwear. Levi's jeans suit me, but I'll go try on styles first to work out what I want to hunt down more cheaply.
Oh, one thing I recommend you do if you like the look of something, especially if the photos aren't clear/there aren't any photos of an item on a model (Vinted photos are often so utterly shit!!). Take a screenshot of the best picture of the item, then do a Google search for the image. It will often show you the item being modelled (not just crumpled on a coat hanger), & give you a much better overview of how it looks being worn. And, say, what length it comes to on someone 5' 8". And if the straps are cut so that you can't wear a bra. All very useful things to find out - before you buy!!!