OP, I get it, even if quite a startling number of posters here don't seem to.
You explained it very well and clearly here.
OBVIOUSLY the OP isn't complaining about those who copy her work as a one-off for personal use (well she might have been but has made it clear it's the CFs who are copying and then selling on that are the real objects of her ire). It's irritating if someone copies something slavishly that you made, even in 'homage' or as a gift for one person, but that does happen. I once made a gorgeous felt Christmas ornament (and yes, it was inspired by stuff I'd seen on Pinterest! but not directly copied, it was my own design that I'd drawn out a couple of times in rough) and put it on my personal FB, and promptly someone I knew made an EXACT copy in felt, down to the embroidery on it, as (I think) a teacher gift. She wasn't selling it but I had to explain to her that IF I'd ever felt like developing the design (which was mine, though not strikingly original) and selling it online or selling the pattern, then her photos all over FB, Twitter etc wouldn't help matters!
But clearly the OP is talking about an original design she's researched, experimented with, tweaked, changed and developed. These are all stages in designing something. If they're sidestepped by someone going to the end product and ripping it off, for a start you can normally tell as the finished item doesn't really look 'right' (maybe because the person ripping it off hadn't spent all that time developing it) but also, that CF is basically stealing all the time and skill and effort you spent in developing your item, as well as the look of the finished design!
I'm a crafter. I do a lot (knitting etc) for fun/pastimes but I do also design and make jewellery, and also decorative items in a medium I'm not naming because it's searchable! There is someone I know slightly in the immediate area who has made these for a lot longer than me. I always wanted to make them and started over the lockdown. I do now sell them in a very limited way. She's been quite prickly about it and turned up at a recent 'open house' thing and almost told me to stop it - despite our styles being very different (and modes of manufacture too - I take a lot of time on mine and she's said in the past she goes for the 'fast and furious' mode of production for her bread and butter pieces. It shows, but I suspect most customers don't notice or care. She can make 5 pieces for one or two of mine of comparable size, so my business plan is crap! 😂 ) Anyway, I try really really hard with this new 'line' of items to make them as different in details from those I see on Instagram etc. It's hard. Everyone makes these items in the following shapes (which sell) - hearts, birds, stars
(god this is sounding properly naff!) so if I want to do those, I do try to make them different. It's a design challenge to keep different and keep flexible and ahead of the game, and that's something that a CF who rips things off just doesn't get.
The posters who are saying 'well if you post your things online to sell with photos, you only have yourself to blame' can get in the sea.
It is WRONG to steal someone else's idea for profit. If you sell online it makes you very vulnerable, but that isn't an open invitation for CFs to rip you off.