Please tell me some tips about how to hire a best trainer for myself? What are the main things to ask for and how to check if they are genuinely experienced trainers ?

Probably a demo, trainer's communication skills, trainer's approach towards the subject in demo class where he should make the student feel like the subject isn't tough, and all it needs is little effort from the students perspective.

Secondary: His certifications on the subject and past teaching experience.

1) You can check their content or lectures on public platforms such as YouTube etc. Trainers often post demo sessions on such platforms. Alternatively, you may seek a demo.
2) You may ask about their previous experience, referrals. You can tally the same from LinkedIn.
3) You may ask domain-specific doubts and assess the trainer.

 1.Ask for guidance and job scope.

2. Understand skill and project.

3. Ask for demo and session wise training plan

4. Ask who will be the trainer and availability and talk to trainer also

5. Ask for duration for training and duration for project, kind of project you do.

6. Ask for tips and guidance after the course if required.

7. Ask for temporary work assignments if any immediately after the course.

8. Ask for job referral if any after the project completion.

9. What else you need , get started online / classroom training with us.

10. Call for clarification and discussion immediately

You can ask the trainer for a demo class, and you can judge his teaching skills. Also, his past teaching experience can be considered. You need to understand the concepts from the trainer in the subject you are about to take the training. See if he can clarify your doubts without any hesitation and see if the session is interactive or just monotonous.