Over the last seven years my lady has had Three UK visas, Two Australian visas and One Schengen Visa. Her experience in obtaining these visas has been that the most valuable document is the statement from her employer showing position, length of service and salary. This is paramount. Also payslips and bank statements are required. As others have indicated some evidence is required to show people have a solid reason to want to return to Thailand. She just got her third UK visa two weeks ago, and it took about five days. With her previous visa history she's looked upon as a no-risk applicant. Never used an agent. Just full in the online application which is very easy and submit the required documents
Not everybody is as helpless as you! We've managed to get to 50 years of age, so filling in a few forms and getting some photocopies is within most people's mental capabilities 😆