I would recommend doing a web search on any company you consider, using search phrases like these (randomly using Sitel's name just as an example)-
Sitel complaints
Sitel scam
Sitel employee complaints
Note also that with most of these companies you are probablyu considered an "independent contractor", so are fully responsible for all your state and federal employee and company tax reporting and withholding and such, and of course probably do not get health benefits of any sort.