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.
An attractive resume template/outline makes it more powerful. Just as dressing smartly helps a candidate in an interview good formatting does the same for a resume. Looks do matter at all places in the real world and on paper. When you present yourself well you get noticed. Similarly when you present a good resume it will be noticed; otherwise it would be very easily find a bin to rest in.
To distinguish the good resume writing services from the bad ones you need to find out how they proceed with the task. A good service asks you to fill out an online question. They also set you up for an interview with the writer. This ensures that the writer is aware of all details that must be present in your resume. If a personal interview is not possible they may also provide you with other ways to get in touch with the writer.
Focus on achievements Employers not only want to know what you have done in the past they also want to know where you have excelled. If you have awards achievements or on the job highlights make sure to add them. If you were part of a team you were part of the success. If your project increased production by 20% and you played a part in it add it on your resume!
The cost is too good to be true. It is only human to try to find the best service at an affordable price. However it is also true that you get what you pay for. If a service says that it can write your resume for a few dollars it is better to be cautious. Creating good quality resumes requires using specific skills. The cost can be lower only if the summary of your career is part of a mass produced set of similar documents.