Reklamacja trwa dłużej niż zwykły zwrot, dlatego wolę najpierw sprawdzić wszystko w przymierzalni.

In Polish, trwać means to last / to take (time). So Reklamacja trwa dłużej literally means A complaint procedure lasts longer or takes longer.

Using jest would describe what something is, not how long it lasts. So:

• Reklamacja trwa długo. = The complaint process takes a long time.
• Reklamacja jest długa. = The complaint process is long.

Both can make sense, but trwa dłużej is the most natural way to talk about how much time the process takes.

In everyday shopping Polish, reklamacja means a complaint or product claim, usually when something is defective and you ask the shop to repair, replace, or refund it.

It is different from zwrot:

• zwrot = a return, usually because you changed your mind or the item does not suit you
• reklamacja = a complaint because something is wrong with the product

So this sentence contrasts a complaint process with a regular return.

Because dłużej is an adverb, not an adjective.

Here it describes the verb trwa (lasts / takes), so Polish uses the adverb:

• długo = for a long time
• dłużej = longer

Compare:

• To trwa długo. = It takes a long time.
• To trwa dłużej. = It takes longer.

But if you describe a noun, you use an adjective:

• dłuższy proces = a longer process
• dłuższa reklamacja = a longer complaint process

Niż means than in comparisons.

So:

• dłużej niż zwykły zwrot = longer than a normal return

This is the standard word used after comparatives such as:

• większy niż = bigger than
• szybciej niż = faster than
• drożej niż = more expensively than

So niż is simply the Polish word that introduces the second part of the comparison.

Because zwrot is a masculine noun, so the adjective must agree with it.

• zwykły = masculine singular
• zwykła = feminine singular
• zwykłe = neuter singular

Since zwrot is masculine, we say:

• zwykły zwrot

Other examples:

• zwykły sklep = an ordinary shop
• zwykła rzecz = an ordinary thing
• zwykłe pytanie = an ordinary question

Dlatego means therefore, that’s why, or for that reason.

It connects the first idea to the result:

• Reklamacja trwa dłużej niż zwykły zwrot, dlatego...
• A complaint process takes longer than a normal return, that’s why...

It is very common in spoken and written Polish.

A useful pattern is:

• X, dlatego Y. = X, therefore Y.

For example:

• Jest zimno, dlatego zostaję w domu. = It’s cold, so I’m staying home.
• Nie mam czasu, dlatego nie przyjdę. = I don’t have time, so I won’t come.

After woleć (to prefer), Polish often uses an infinitive, just like English uses to + verb.

• wolę sprawdzić = I prefer to check
• wolę poczekać = I prefer to wait
• wolę zostać = I prefer to stay

So wolę najpierw sprawdzić wszystko means I prefer to check everything first.

This is about aspect, which is very important in Polish verbs.

• sprawdzać = imperfective, focusing on the process / repeated action
• sprawdzić = perfective, focusing on completing the action

Here the speaker means check everything once, fully, before buying/returning. That is why sprawdzić is natural.

Compare:

• Muszę sprawdzić rozmiar. = I need to check the size.
  (one complete check)
• Zawsze sprawdzam metki. = I always check the tags.
  (habit / repeated action)

So wolę najpierw sprawdzić wszystko suggests one complete check before taking the next step.

Najpierw means first or first of all.

In this sentence:

• wolę najpierw sprawdzić wszystko = I prefer to check everything first

Polish word order is fairly flexible, so najpierw can move around, although some positions sound more natural than others. For example:

• Wolę najpierw sprawdzić wszystko.
• Najpierw wolę sprawdzić wszystko.
• Wolę sprawdzić wszystko najpierw.

The version in your sentence is very natural because najpierw sits right before the verb it modifies.

Wszystko means everything.

It is a neuter pronoun and often stays in this form when used as the direct object:

• sprawdzić wszystko = to check everything
• widzieć wszystko = to see everything
• zrobić wszystko = to do everything

So here it simply functions as the object of sprawdzić.

Because after w meaning in for location, Polish uses the locative case.

The basic noun is:

• przymierzalnia = fitting room / changing room

In the locative singular, it becomes:

• w przymierzalni = in the fitting room

This is a normal pattern for many feminine nouns ending in -a:

• kuchnia → w kuchni
• łazienka → w łazience
• przymierzalnia → w przymierzalni

So the ending changes because the preposition w requires the locative here.

It literally means in the fitting room, but in context it can also suggest while I’m in the fitting room.

So the idea is:

• the speaker wants to check everything there, before leaving or before needing a later complaint/return

Polish often uses simple location phrases in places where English might use a fuller expression like while I’m in the fitting room.

Yes. Polish word order is much more flexible than English, because endings show grammatical relationships.

The original sentence is natural:

• Reklamacja trwa dłużej niż zwykły zwrot, dlatego wolę najpierw sprawdzić wszystko w przymierzalni.

But other versions are also possible, for example:

• Dlatego wolę najpierw sprawdzić wszystko w przymierzalni, bo reklamacja trwa dłużej niż zwykły zwrot.
• W przymierzalni wolę najpierw sprawdzić wszystko, bo reklamacja trwa dłużej niż zwykły zwrot.

Changing word order usually changes emphasis, not the core meaning. The original version sounds balanced and natural.

It sounds like natural, standard Polish. It is not overly formal, but it is also not slangy.

A native speaker could realistically say this in a shop-related context. The vocabulary is practical and normal:

• reklamacja
• zwrot
• sprawdzić
• przymierzalnia

So it is a good example of everyday spoken or written Polish related to shopping.