That is a very bold guarantee to make when they know very little about your vertical or targeted keywords.
As an SEO that has worked in an agency for high profile clients, as well as in-house in very competitive verticals, one thing that I steer clear of for all of my previous clients and management team is guaranteed results. SEO is just too volatile in my opinion.
On the other hand, I feel like I can outrank any SEO out there if I have the time and budget. And the proposal you got just seems to be too short of a timeline for too little budget.
It is most likely too good to be true. And even if it does work, there is no telling how long it will last.
If you have any SEO skills, I'd recommend optimizing your own sites and investing that money in quality content (long form or something backed by actual research or a survey). As you get your content and optimization together, you can then take steps to get some authoritative links (which you can easily invest in here on BHW).
