If someone tells you they can guarantee a certain amount of traffic within a certain timeframe I can promise you one of two things: They are lying, or they plan to cheat and run the risk of getting your site banned or de-indexed.
I have brought websites out of the gutter before, but before I would commit to anything, or take any sort of payment I would need to poke around under the hood a bit (see your data, and check out your website and competitor) Organic traffic comes from rankings more or less. My best strategy is to find a way to provide something on your website that a user couldn't get anywhere else. Not knowing what the site is about, or what it represents makes it difficult to provide any more details than that.
If this is a journey you are interested in talking, let me know. I have just recovered from a radial nerve injury and I don't have a lot on my plate at the moment. Just be careful of scammers who will take your money, bump your traffic for a week and then get you banned.