Well, i have tried this before and this is my result.
Me: Can you rank this website to first page?
Seller: With Package ABC + Package DEF, you will get your desired ranking.
Me: ok, bought both packages.
2 month later no result:
Me: hey mate, there is still no movement since 2 months yet, links are not even indexed.
Seller: We don't guarantee any ranking.
That is pretty much what happen to me (True Story), expectation in these SEO packages can only be learnt through experience, you buy a lot, you experience a lot then you know what to expect. Bare in mind, most sellers will try to close you, not to rank your site. So they "tend" to give you good expectation but still "no guarantee", my suggestion is using your due diligence, buy more and track each of their performance, this is how i churn out a few good suppliers.
Just my 2cent though
