Learn Finnish: Tiedustelimme hintaa myyjältä. - We inquired about the price from the seller.

This is the core rule for verbs of asking! Verbs like tiedustella (to inquire) and kysyä (to ask) demand that the person you are asking is in the ablative case (-lta/-ltä). In Finnish, you literally ask a question "from" someone.

Why is the price in the partitive case (hintaa)?

The verb tiedustella requires the thing being asked about to be in the partitive case. So the formula for this verb is: tiedustella + partitive (the thing) + ablative (the person asked).

How do we form the past tense tiedustelimme?

Tiedustella is a type 3 verb. To form the past tense (imperfect), take the consonant stem (tiedustel-), add the past tense marker -i-, and finally attach the personal ending -mme for "we".

Could I just use kysyimme instead of tiedustelimme here?

Yes! Kysyä is the standard everyday verb for "to ask", while tiedustella is a bit more formal, translating closer to "to inquire". They both use the exact same grammar rules, so Kysyimme hintaa myyjältä is perfectly correct and means the same thing.