البائع قرب الدراجة المستعملة.

It is a nominal sentence in Arabic, not a verbal one.

• البائع = the subject/topic of the sentence
• قرب الدراجة المستعملة = the predicate, telling you where the seller is

So the structure is roughly:

• البائع = the seller
• قرب الدراجة المستعملة = near the used bicycle

In traditional grammar, قرب الدراجة المستعملة functions as an adverbial predicate of place.

Because in Arabic, the verb to be is usually not expressed in the present tense in sentences like this.

So Arabic says:

• البائع قرب الدراجة المستعملة

where English says:

• The seller is near the used bicycle

This is very normal in Modern Standard Arabic. If you wanted the past or future, then Arabic would use a verb, such as كان for was.

Here قرب means near and works like an adverbial noun of place rather than a simple preposition in the same way English uses near.

A helpful way to think of it is:

• قرب + noun = near + noun

So:

• قرب الدراجة = near the bicycle

In grammar terms, قرب is often treated like a ظرف مكان (an expression of place), and the noun after it comes in the genitive.

Because قرب is followed by a noun in an iḍāfa-like construction here.

So in full grammatical form:

• قربَ الدراجةِ

The word الدراجةِ is genitive because it is the noun attached to قرب.

That is why, if full case endings were written, you would expect:

• البائعُ قربَ الدراجةِ المستعملةِ

Even though everyday Arabic writing often leaves those endings unwritten, the grammar is still there.

Because Arabic adjectives normally come after the noun they describe.

So:

• الدراجة المستعملة = the used bicycle

not:

• المستعملة الدراجة

This is one of the biggest word-order differences from English. In Arabic, the usual order is:

• noun + adjective

Because it describes الدراجة, and دراجة is a feminine noun.

Arabic adjectives must agree with the noun they describe in:

• gender
• number
• definiteness
• case

Since الدراجة is:

• feminine
• singular
• definite

the adjective must match it:

• المستعملة

If the noun were masculine, the adjective would be masculine too.

Because when an adjective describes a definite noun, the adjective must also be definite.

So:

• الدراجة المستعملة = the used bicycle

Both words have ال, because the bicycle is definite and the adjective agrees with it.

Compare:

• دراجة مستعملة = a used bicycle
• الدراجة المستعملة = the used bicycle

This is a very important rule in Arabic adjective phrases.

Yes, it functions as a noun here, meaning seller, but it is originally an active participle.

It comes from the verb:

• باع = to sell

And بائع literally means something like:

• selling one
• or more naturally, seller

So البائع means the seller.

This is a very common pattern in Arabic: active participles often become ordinary job or role nouns.

The د in الدراجة is a sun letter, so the ل of ال is not pronounced clearly.

So it is pronounced more like:

• ad-darrāja

rather than:

• al-darrāja

This is normal with sun letters. The spelling stays the same, but the pronunciation changes.

Yes, unvowelled Arabic can sometimes be ambiguous, and قرب is a good example.

Without diacritics, قرب could potentially be read in more than one way in isolation. But in this sentence, once the meaning is known, the intended reading is the one meaning near.

So learners should know two things:

• Arabic script often leaves short vowels unwritten
• context usually tells you which meaning is intended

That is a normal part of reading Arabic.

Yes. A very common alternative is:

• البائع قريب من الدراجة المستعملة

This uses:

• قريب = near
• من = from/of

Another common style is:

• البائع بالقرب من الدراجة المستعملة

All of these express roughly the same idea, but the original sentence is a compact, perfectly valid Arabic way to say it.