There are many academic writing services (editing, proof reading and writing from scratch). These services range from writing basic essays to research papers and dissertations. I will use editing and proofreading services because my mother tongue is different from the language of thesis. I distrust these kinds of services, can they really do job appropriately and according to suitable form? Is this considered plagiarism and can they write in an original fashion? Has anybody used these kind of services and what are your experiences?
There's a big difference between paying someone to proof read your thesis (generally acceptable, and sometimes encouraged) and paying someone to write original material from scratch (plagiarism).
The way your question is worded (and from one of the comments about getting someone to "edit and write the thesis") it sounds like you are asking whether if you pay someone to write part of your thesis, will they do it well enough that it wont be detected by plagiarism software (e.g., the idea that people who write paid essays just copy and paste huge chunks from Wikipedia and random journal articles). My apologies if this is not what you are asking. But to state the obvious point, paying someone to write your thesis and contribute intellectually is plagiarism and unethical whether they do it in a rigorous or a sloppy way. It is plagiarism, because you are not acknowledging the source of the intellectual effort.
Surely if you are paying someone merely to refine your expression, phrasing and give general guidance on structuring, then there is minimal risk of plagiarism.
Using a service that edits documents to correct grammar and spelling issues, and minor awkward phrasings, is acceptable and need not be acknowledged.
Using a translation service, to translate a document from your native language into English, is acceptable, though the translator needs to be prominantly acknowledged. If you can write in English, though, it may be better to do so, because many employers in academia may be wary of applicants who have not demonstrated high-level proficiency in English.
Using a "substantive editing" service, that re-writes a document to improve its logic, flow, general structure and rhetoric is problemmatic. Such an editor should probably be named as a co-author, but if not, needs to be very prominently acknowledged. The use of such a service may not be acceptable to those evaluating the thesis.
Using a writing service, where you provide your results and they write the document without working from a strong draft from you, is cheating, and not likely to be acceptable even if acknowledged.
There are two issues. The first is, if the "academic writing service" did genuinely original work for pay and let you sign your name to it, would it be plagiarism or copyright violation? In a "corporate" setting, the answer would be "no," because it was "work for hire," to which the payor owns the rights. But in an academic setting, it would be plagiarism, because you are representing work done by others as your own work, and thereby overstating your capabilities.
The second issue is, can these services produce work that is sufficiently original not to violate copyright or constitute plagiarism. The answer is usually no. The reason is, unlike the situation with a corporation that will "pay what it takes," these services usually "shortcut" to keep their fees down. But this issue is "trumped" by the first one in the previous paragraph.
In my university proofreading would be somewhat. Editing would normally not be acceptable. The reason is that the thesis assesses many aspects of your abilities. That includes not only your ideas (intellectual skills), but also your ability to express your ideas clearly, and even your ability to express yourself in (in this case) English (transferrable skills).
Getting someone to read through your work and identify typo's, runaway sentences and other little snafus is normally fine (and impossible to identify as well). On the other hand if someone corrects the way you structure your sentences, paragraphs and sections that is not appropriate. If however you use university resources (your thesis adviser perhaps, and/or library services) you will not need to worry about it being acceptable. At that point it is the university that is responsible for ensuring your learning experience.