Learn French: Le concessionnaire garantit la fiabilité malgré le kilométrage. - The dealer guarantees the reliability despite the mileage.

Fiabilité comes from the adjective fiable (reliable), which is derived from the pronominal verb se fier à (to trust). The suffix -ité is used to form abstract nouns from adjectives, similar to "-ity" in English.

Why do we use malgré here instead of bien que?

Malgré (despite) is a preposition and must be followed directly by a noun or pronoun, like the noun le kilométrage in this sentence. If you wanted to use bien que (although), you would need to follow it with a full clause containing a conjugated verb, usually in the subjunctive.

Why is there an acute accent in kilométrage but a grave accent in kilomètre?

This is a spelling rule based on syllables. The grave accent (è) is used when the vowel in the next syllable is a silent "e" (as in ki-lo-mè-tre). By adding the suffix -age, the next syllable no longer has a silent "e", so the accent changes to an acute accent (é).

What conjugation group does garantit belong to?

The infinitive is garantir (to guarantee). It is a regular second-group verb ending in -ir. This means it behaves like finir, where plural forms receive an extra -iss- stem (for example, nous garantissons).