Most companies, SEO or Web development, have had to deal with a client requesting that they give a 3rd party SEO company FTP access to their site. Basically, a client registers a new .com, that list is used by dozens (if not hundreds) of companies to pitch different online services. The client gets a phone call or email from an SEO firm, promising outstanding rankings. The client wants to go with the SEO firm but the SEO firm needs FTP access. You as the person who manages the site, as the person who has the keys to the site, are you willing to give this seo company access?
That is the topic of a thread at HighRankings forum named Seo "expert" Hired By Client -do I Give Ftp Acces, What do others do.
Let me tell you what I would do.
(1) Research this SEO company and if everything seems good on the outside... (2) Schedule a conference call with the SEO company and the client. (3) Then explain the pros and cons of using this SEO firm, if the client wants to proceed with the SEO firm (4) Set up a plan for the SEO firm to work off of a development environment, so all changes can be first reviewed by me. (This can be as easy as having the SEO firm write up a list of changes or setting up a versioning system to track changes). (5) Review changes and make suggestions to client, with client approval... (6) Upload changes.
If the SEO firm demands full FTP access, I would tell the client to host the site on some other server (especially if it is a shared box).