I would never advocate gambling, but if one is going to do it, I suggest doing it using a betting exchange such as Smarkets. Whole new level of crazy betting at a traditional bookmakers these days in my view, now that exchanges have appeared. There is no bookies spread on an exchange (better odds, lower cost overall), they don't bombard you with gambling adverts, teasers and false promos to hook you like traditional bookies, they don't deliberately make keeping track of your losses difficult like bookies do, and they don't give you shit if you have winnings to collect, as far as I know.
Oh, and bookies really get their pound of flesh with cash-out and stuff like that, relatively speaking. That's why they try and get you to do it and make the cash out buttons so easy to accidentally hit. If you are looking to 'lock in' profits like that from long odds bets before they are settled (eg. take advantage of your 100/1 odds bet, even if they don't actually end up winning the final), in my view you're better off doing the 'opposite' side of betting (once you have laid the initial bet of course, and the odds shorten), again using the exchange, which is called 'laying'. It's basically where you act as the 'bookie'. You can use that to take advantage of such bets where the odds shorten over time, so you don't lose everything even if they don't win. You have to learn a bit about how it works so you don't accidentally lay too much, but it's not all that complicated. PM me or post here if anyone feels I may be able to help with some question about that stuff (or have a different point of view on exchanges).
Examples are Smarkets SBK, Betfair Exchange, and Betdaq. Smarkets SBK seems the best one to me.
No vested interest here - I just detest how shady and full of BS bookmakers are (and the regulators) and how cynically they screw people over.