How do you prevent getting ripped off by a dodgy builder happening to you?
Firstly - a personal recommendation and sight of their work is worth 100 reviews on a tradesperson finding website which is basically paid advertising. Ask yourself why this person is advertising for work regularly and on different platforms. The good ones are booked up well in advance and don't need to advertise.
If they have a limited company, fgs look up that company on the Companies House beta service. It is completely free. If the company is relatively new and has overdue filings, tread very carefully. Look at the people related to that company. Look at how many past directorships of dissolved companies they have. Did those companies not file accounts or compliance statements (formerly called annual returns)? If there's a pattern there, avoid. Yes, it's a pain trying to find a decent tradesperson who can do your job roughly when you want it doing, but it's a lot more painful losing your savings or paying off a loan which you have nothing to show for.
If they claim to be a member of a trade body, check with that body that they are on their register. Report them if they are not.
Anyone who is using their limited company name to get your business should have a company bank account. It's one of the things the first board meeting of the company decides. Do not pay into that person's personal bank account. At the very least they are possibly on the fiddle re: tax. At worst, they just want your money to fund their holiday, their gambling addiction, etc. A bona fide company director will have no issue with you paying the company. If at all possible, pay at least some of the money by credit card as it affords you some protection. Writing a cheque which they have to pay in is better than making a bank transfer because they have to play a part and it shows their intention.
If you ask questions and don't like the answers or you smell a rat, trust your instincts.