A golden rule: no legitimate company will ask you for money before hiring you, period. If you see requests for payment for certificates, courses, or "skills verification," it's 100% a scam - run away immediately.
For trustworthy sites, search on LinkedIn directly from official company pages (not from random recruiters), or use FlexJobs, We Work Remotely, or similar platforms that filter job postings. Before sending your CV, always check: does the company actually exist? Do they have a professional website with real contact info? Is the salary realistic for the role, or does it sound too good to be true? If they ask you to communicate only via WhatsApp or Telegram, or if the conversation is full of weird typos, don't trust them. Ask the recruiter a couple of pointed questions about the project or the company - someone legit will answer with concrete details, while a scammer will copy-paste generic responses.