I had a Surgeon that hired us to do his SEO 3 months ago. After we went thru his site and removed all of the error codes that existed from the other companies SEO Marketing his site jumped right back up as high as it was in a matter of 45 days. Now he is even higher. 

Now this is not always the norm but it does happen when you have been high and all of a sudden drop just a bit and stay there. 

Remember if the company that is doing your SEO uses Marketing pages, if and when you ever leave their services they WILL remove the Marketing pages. 

But don't worry it's ok because most companies SEO Market your site not pages that you do not even own. 

We do the work to your site not pages of our own. No you do not have to start over at all if you switch and it will happen quickly.