"I would like to buy two blue ties."
Translation:Haluaisin ostaa kaksi sinistä kravattia.
In the sentence "Haluaisin ostaa... +object", there is nothing that requires the partitive case (it's not negative, it's not an incomplete action, ostaa is not one of the partitive-requiring verbs, etc.) - that's why the object is in accusative and "kaksi" just remains "kaksi". The rest of the expression - "sininen kravatti" must be in partitive simply because it follows an amount (two). Compare this with "I'd like to buy ONE blue tie": ..."Haluaisin ostaa yhden sinisen kravatin" - now the whole object is in accusative (which shares its actual form with the genitive).
If you say the same sentence in negative, you'll have the whole object in partitive: "En halua ostaa kahta sinistä kravattia". If you use a partitive-requiring verb, the same things happens: "Etsin kahta sinistä kravattia" (I'm looking for two blue ties - looking for something is by default an incomplete action.) If we do this with "ONE blue tie", we still get the partitive: "En halua ostaa (yhtä) sinistä kravattia." and "Etsin (yhtä) sinistä kravattia."
Ymmärrätkö nyt? :)
Yes, the previous example is also missing the core verb of the sentence. It shows even in Beta, no one is really testing this.
The only verb option following "Haluaisin" is "sovittaa". It should be "ostaa". If I go to a store in Finland and say "haluaisin [jotain]" it is probably understood that I would like to purchase that thing. However, if the translation is explicitly expressing the idea that these ties are to be bought, that verb should be used (i.e., "ostaa").
No buying involved in the Finnish. Could it be correct in the context of being in a store at the counter and saying this?