No, posting certificates on LinkedIn is never bad no matter where you did the course. Recruiters pay more attention towards your knowledge rather than your course’s certification platform.
Certificates are a proof that you have tried successfully to acquire a new skill. This skill may be a hard skill such as Python programming or a soft skill such as Effective Communication. All of these skills give you some knowledge that you can use in your personal or professional life.
Free Courses From Reputed Institutions
According to Forbes, doing a good research can help you get access to free online courses from reputed institutions.
Most of these courses will charge for a certificate but there are many that are completely for free. Some examples are Machine Learning by Coursera, Financial Markets by Yale, Psychology Course by Yale, etc.
In my experience as a professional since the last 3-4 years, recruiters hardly take a deep look at who has issued your course certificate. All that matters is how deeply you understand this field. They can easily check, by asking simple questions, as whether you have really worked towards the course or just have cheated to get a branded certificate.
Further, no recruiter takes a deep look at your certifications unless you are a fresher.
For professionals like me, online courses are a way of letting others know about my knowledge.