How long usually you can see result from SEO services?

Such a brought question. Depends on your investment, time and effort. There is no guarantee that you can see results within one month.
Rank depends exclusively on the competition, it doesn't have to be exclusively related with money or investment. If there is no competition then ranking is real easy. If competition is tough like "itunes" or similar then not money nor time will help, it will take time and money and effort.
Never because they're crap and they don't work. Use the services where people create the properties for you then you control everything, that's the only way. Not even a single "service" provider will give you anything better than 1 star garbage UNLESS you take full control and approve every step of the process: the article, the site the link goes onto, etc. etc. If I wanted to rank a blackhat site I would perhaps consider the PBN services but it's better to do your own if you don't mind paying the hosting and domain and all of that.

Never point a "service" at anything you want to survive an algorithm update, only point at throwaway sites.
It takes longer to see results than it used to for sure. You need a bit of patience sometimes these days.
Depends on the keyword, the competition, which SEO provider you went with, if they actually did their best work, many factors are involved in this.

It's hard to give a definite answer of when you'll see amazing results.
In every way it depends your Site's current SEO structure.. If you have some good past link history and you are just increasing in diff strategy 2 month is max ...But if you are starting fresh, it will take some time depending on your niche... The question you have brought in is quite broad and no one cant answer it perfectly ..

It just depends on what you are doing to help optimize it. IF you are putting in a lot of time, then it will not take as long. One month may be doable for some.
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