I recently came across the Duolingo question of "They sell a lot of spices and oils." The translation was, "Ili vendas multe da spicoj kaj oleoj." After looking at the discussions about the usage of multe vs multa, I became confused. Is there a difference between them at all? Thank you!

According to PV, the two forms are synonymous.

You also can say:

...multon da spicoj kaj oleoj

I see, thank you! Would there be a difference in emphasis or implication if one was used over the other?

multa

The basic word is the adjective multa for which PIV (Plena ilustrita vortaro) gives three definitions. All English translations are mine and thus might be off, but I hope you get the idea.

1) large undefined quantity of a whole which one cannot enumerate

● la tro multa parolado lacigas lin : the too much speech makes him tired

2) (in plural) large undefined quantity of enumerated things in contrast to a small quantity

● el multaj milonoj fariĝas milionoj : many thousands make a million

3) (when the noun is left out) large number of people

● multaj serĉas favoron de reganto : many seek the favour of a regent

From that definition 2 follows that you can say Ili vendas multajn spicojn kaj oleojn.

multe

The adverb multe is a derivative and it too has three definitions.

1) used to show a long lasting or a repeating action

● ne multe dormi : do not sleep a lot

2) used to show that an action concerns a large quantity or is relatively intense

● kiu multe profitas, ankaŭ perdon ne evitas : he who earns a lot, cannot avoid a loss

3) used to emphasise the comparison

● kio multe kostas, multe valoras : which costs a lot, values a lot

In order to use an adverb to describe a noun you have to use da (which in essence is a partitive marker). Thus you can also say Ili vendas multe da spicoj kaj oleoj.

and the difference is?

Given those definitions that the adjective describes the quantity direct and the adverb describes the action, you get the following translations.

● Ili vendas multajn spicojn kaj oleojn : They sell many spices and oils (there are several sorts of spices and oils)

● Ili vendas multe da spicoj kaj oleoj : They sell a lot of spices and oils (they sell a lot, nothing is stated about how many sorts)

Remark 1

I bet that in practice these get mixed by many speakers.

Remark 2

A warning to the English speakers! The pronoun ili in Esperanto always refers to some defined persons (or things), referring collectively to the personel in a store is ok. Ili cannot be used in the passive voice way as in English, for that purpose use vi (you) or oni (one).

These have the difference that vi requires that listener is capable of performing the action. For instance, you visit your friend and see that there are paint buckets and stuff next to the wall, so probably the house is getting painted, even if nobody is actually painting right now ). You cannot say Vi farbas la domon if your friend is severely handicapped and cannot hold a brush.

Ah, I see! So multaj means that there are a lot of individual things, so it means that there are a lot of different spices. Thank you!