The website for UK VFS has under User Pay Services, a service they call "Get It Right":

 

"Have your completed application checked by VFS staff before it is sent to UKVI for processing.

Customers who have completed and printed their application form can pay an additional fee to have the documents checked by VFS staff before it is sent to UKVI for processing.  Staff shall check that documents are complete as per the checklist provided by UKVI before sending it for processing.

If VFS staff finds that there are missing documents, customers will have the option to submit these in person at UK Visa Application Centre after their appointment, within 3 working days. Using the ‘Get It Right’ service does not imply or guarantee that applications will be successful.

This service costs an additional THB 350 per applicant and is available to customers applying at UK Visa Application Centre."

My last visa application was July 2015. I thought this what the VFS staff have always done for no charge when you submit your documents. Has something changed since then?

 

Just another source of revenue for them. I wouldn’t trust VFS staff to check any application visa documents...