Question: I am looking for a single word to describe a group of customers, who merely take advantage of the company's services (they come only for free period and leave afterwards or take the gift and leave again).

So far I came up with a term `Profiteers`, but this is somewhat pejorative, which is not what I want.

Answer: 
I think the word you are looking for is Sampler, from [Merriam-Webster](https://www.merriam-webster.com/dictionary/sampler). It's certainly non-pejorative, and many retailers, such as Amazon, refer to their giveaways as Samples (in their Kindle Books section).

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> Definition of sampler 
>  1
>  :  one that collects, prepares, or examines samples
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[Transient(s)](https://en.oxforddictionaries.com/definition/transient) might fit your needs:

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> ADJECTIVE
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> 1. Lasting only for a short time; impermanent.
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> 1.1 Staying or working in a place for a short time only.
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and

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> NOUN
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> 
> 1. A person who is staying or working in a place for a short time only.
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