How Do I Choose a CV Resume Writing Agency? Worth Paying for One?

Hi everyone,
I’ve been job hunting for a couple of months and I’m not getting the response I expected. I’ve sent out a lot of applications and had only a couple of interviews, which makes me think my CV is holding me back. I’ve been looking into hiring a CV resume writing agency, but there are so many options that I don’t know how to tell the good ones from the rest.
Some of them look polished but I suspect they just put your details into a template. Before I spend any money, I’d love to hear from people who’ve done this:

• Did using a CV resume writing agency make a real difference to your interview calls?
  
• How can I tell whether a proper writer works on my CV or whether it’s just a template?
  
• Is there usually a consultation or questionnaire first, and is it a red flag if there isn’t?
  
• How many revisions are normally included, and are changes charged extra?
  
• Do agencies tailor the CV to your industry, and can they help with ATS formatting?
  
• Do they also offer cover letters and LinkedIn profile help, or is that a separate charge?
  
• What’s a realistic price range, and does a higher price mean better quality?
  

I’d also welcome any warnings about agencies to avoid, like ones that guarantee jobs or push you to buy straight away. If you’ve rewritten your own CV with good results instead, I’d love to hear how you did it.
Thanks in advance, honest feedback (good or bad) is much appreciated!