In the first place you need to know what your site needs, and then find someone who provides that particular service. Many of these people tell you right in their sales thread they are using spin stuff, or whatever. As long as they give you what they said they will they have fulfilled their end.
Buying a link blast when you need on page seo is not going to rank your site. Buying on page seo when you need quality backlinks is not going to help.
A good example of someone failing to do this is Rayee above. He is buying services that are not proper to rank a local site, and he blames the seller.
If you do not know what you need, throwing backlinks at something is stupid and hoping it will help is ever more stupid.
Amother thing, what is fine right now may be not allowed in a few months. Compounding this is the fact that something that is working now but is Blackhat (people will call this grey hat) at some point may get you penalized.
If you do some grey hat stuff, and later buy a package, the grey hat may bite you in the ass and you blame the seller of your last service. Since you have no idea what you actually need, nor what actually happened, its hard to blame anyone,except yourself.
When you go buy a car, do you tell the salesman to get you a car, or tell them that you need a car for a family with a trailer hitch for pulling as boat? If you do not even know what kind of car you need, you need to do some research into what you need, and find a car that fits that need. If a sales man told you that he has a volkswagon that will pull a 30 ft boat, and get 1000 miles a gallon while doing this, would you buy that car? No, because you know damn good and well it cannot do it. Buying services is the same way.
Another thing: SEO literally changes from moment to moment, and any time your site behaves in a way that your competitors do not, it can raise flags. Local businesses do not typically have a lot of backlinks. Blasting a local site like this can kill it, because they do not behave that way.
Learn your craft, then buy services you need, test these services until you find the right one for you, or be specific when you order, make the person commit to what you need, and hold them accountable.
There are good services here, and newbies who read a WSO and consider themselves SEOists.
A blanket statement about all services is simply not true.
One could even say you are lying.
This is a buyer beware world, and you need to do your homework.