Avoid being vague If you have references include them. Dont say available upon request. If you have gaps in employment explain them clearly. They will probably come up in the interview anyways. Being prepared in advance by giving complete information in your resume is better than being caught off guard in the interview or worse skipped over all together.
No contact address is available. If the service does not have a physical location they may not be a suitable option for you. The chances are they are more into mass production of average documents. Numerous resume mills employ non-skilled individuals overseas to create these documents. They get hold of your current resume embellish it with the information available from the questionnaire and place it in a standard format.
No sample resumes are accessible. A competent resume writing service will provide a number of samples for review. You can assess the quality of their work only if have these samples. If there are no samples available on their website ask them for the specimens of their work. If they are unable to provide satisfactory examples of their work you had better opt for another service.
The resume writing service does not require knowing anything about you. All they ask you to do is fill out a standard online questionnaire and maybe submit your current resume. A competent service needs you to fill out a questionnaire; however it does not end with this. They contact you and ask for numerous other details about your career and achievements that they need to create an effective resume.
When people apply for positions and send PDFs the employer or recruiter has to open each email download the resume and view it. Since there are many unemployed and underemployed people job hunting there are many job applicants applying for positions and because of the time it takes to view each PDF many applicant resumes may never get seen. When job applicants send a direct link to a resume page its much quicker to view a job applicants resume. If an employer or recruiter likes the resume page they can down the resume right from the resume website site and also view the job applicants complete online profile.