Hi D4,
Rankings are affected by a host of factors, not the least of which are personalization and localization. Given that different people search for different things in the normal course of things, it is quite likely that two different people searching on different computers will get different results.
I would be very cautious about conducting repetitive searches every few minutes as you have described, because in the end, it could be you and your helpers that are influencing what you see in the rankings!
It is important to remember that Google and Bing both utilize click through data from the SERPs to inform rankings. Every time your site is returned in the results, but not clicked-through and every time a searcher clicks through, but quickly returns to the search engine, Google and Bing are gathering information that suggests your site is not seen as relevant or helpful by searchers. Constantly running redundant searches like this could eventually have a negative impact for your site.
I would say that you might be better served by conducting an in depth analysis of the pages concerned and putting the focus on improving them. If you get this aspect right, rankings and traffic will improve naturally over time.
Hope that helps,
Sha