Prodavac meri ulje i vaga krompir.

Here, vaga is a verb: the 3rd person singular present form of vagati, meaning to weigh.

So in this sentence:

• vaga = weighs

But vaga can also be a noun meaning scale or weighing scale. Context tells you which one it is.

Compare:

• Ovo je vaga. = This is a scale.
• Prodavac vaga krompir. = The seller weighs potatoes.

Meri comes from meriti and has the broader meaning to measure.
Vaga comes from vagati and means more specifically to weigh.

So the sentence makes a useful contrast:

• meri ulje = measures oil
• vaga krompir = weighs potatoes

In real everyday Serbian, meriti can sometimes also be used where English would say weigh, so this contrast is a bit neat and textbook-like, but it is still understandable and natural enough.

Both are in the accusative case because they are direct objects of the verbs.

• ulje is neuter singular
• krompir is masculine inanimate singular

In Serbian, the accusative often looks the same as the nominative for:

• neuter nouns
• masculine inanimate nouns

That is why you see:

• ulje not a different form
• krompir not a different form

A useful contrast:

• Vidim krompir. = masculine inanimate, same form
• Vidim psa. = masculine animate, different accusative form

In Serbian, krompir is often used as a mass/commodity noun when talking about the food in general, especially in shopping or market contexts.

So:

• Kupujem krompir. can mean I’m buying potatoes
• Krompiri is used when you mean individual potatoes more clearly

This is similar to how English sometimes uses a singular mass noun for a product, even when the real-world item consists of many pieces.

Because Serbian has no articles. It does not have direct equivalents of a/an and the.

So:

• prodavac can mean a seller or the seller
• ulje can mean oil / the oil / some oil
• krompir can mean potatoes / the potatoes / some potatoes

Context usually makes it clear. If Serbian wants to be more specific, it can use words like:

• ovaj = this
• taj = that

For example:

• taj prodavac = that seller

Both verbs are in the present tense and are imperfective:

• meri = present, imperfective
• vaga = present, imperfective

This can describe:

• something happening right now
• a habitual action
• a general scene

So the sentence could mean either:

• the seller is doing this now
• this is what the seller generally does

If you wanted a completed action, you would normally use perfective verbs, for example:

• Prodavac je izmerio ulje i izvagao krompir.

Yes. Serbian word order is more flexible than English word order.

The version you have is a neutral, straightforward one:

• Prodavac meri ulje i vaga krompir.

You can also rearrange parts for emphasis, for example:

• Prodavac vaga krompir i meri ulje.

That still makes sense; it just presents the actions in a different order.

However, for learners, the given order is the safest and most neutral pattern: subject + verb + object.

Yes, prodavac is grammatically masculine singular.

For a female seller, you would usually say:

• prodavačica

So:

• Prodavačica meri ulje i vaga krompir.

In some contexts, masculine forms can be used generically, but if you know the seller is a woman, prodavačica is the natural choice.

Yes, Serbian often leaves out the subject when it is already clear from context.

So if everyone already knows who is being talked about, you could say:

• Meri ulje i vaga krompir.

But when you are introducing the sentence on its own, keeping prodavac is more natural because it clearly states who is doing the actions.

A rough English-friendly guide:

• Prodavac = pro-DA-vats
• meri = ME-ri
• ulje = OOL-yeh
• i = ee
• vaga = VA-ga
• krompir = KROM-peer

A key point is lj in ulje.
It is a single Serbian sound, not a plain English l plus j. A rough approximation is the lli sound many English speakers use in million.

Yes, in many situations meriti can be used more broadly, so meri krompir may be understood.

But vagati is more specific: it means to weigh, usually with a scale.
So vaga krompir is more precise if you want to emphasize weighing.

That is why the sentence uses:

• meri for oil
• vaga for potatoes

It highlights two slightly different kinds of measuring.