kono mise ha nitiyouhin ga yasui ueni, syanpuu no tumekae mo takusan oite arimasu.

うえに means something like on top of that, in addition, or besides.

In this sentence, it connects two positive points about the store:

• 日用品が安い = everyday goods are cheap
• シャンプーの詰め替えもたくさん置いてあります = they also stock lots of shampoo refill packs

So A うえに B means not only A, but also B.

A rough nuance:

• そして just adds another statement: and
• しかも often adds emphasis: moreover / what’s more
• うえに feels a little more structured and often means on top of that

It can follow:

• verbs: 安い is actually an i-adjective, but it works directly before うえに
• i-adjectives: 安いうえに
• na-adjectives / nouns: usually 静かなうえに, 便利なうえに, 学生であるうえに or 学生のうえに depending on style and construction

This is a very common question about は and が.

• この店は sets the topic: as for this store
• 日用品が安い tells us one thing about that store: everyday goods are cheap

So the structure is basically:

• As for this store, everyday goods are cheap...

Here, は introduces the larger frame of the sentence, and が marks the thing that has the property 安い.

You can think of it like this:

• この店は = regarding this store
• 日用品が安い = everyday goods are cheap

This pattern is very common in Japanese:

• この店は魚が新鮮です。
• この町は夜景がきれいです。

It does not mean there are two unrelated subjects. It means the sentence is describing the store by talking about one of its features.

Because 安い is an adjective, not a transitive verb.

In Japanese, adjectives like 安い, 高い, 大きい, 面白い describe a noun directly, and the noun being described is typically marked by が in this kind of sentence.

So:

• 日用品が安い = everyday goods are cheap

But を usually marks the direct object of an action verb:

• 日用品を買う = buy everyday goods

You would not say:

• 日用品を安い ❌

because 安い is not an action being done to 日用品.

日用品 means daily necessities, everyday goods, or household essentials.

It refers to practical items used regularly, such as:

• soap
• detergent
• toilet paper
• toothpaste
• shampoo

It is a compound:

• 日 = day
• 用 = use
• 品 = goods / items

So the basic idea is items for everyday use.

In this sentence, it refers to the kind of things sold in the store that are cheap.

シャンプーの詰め替え means shampoo refill or shampoo refill pack.

Breakdown:

• シャンプー = shampoo
• 詰め替え = refill / replacement filling / refill pack

The particle の links the two nouns, so it works like:

• refill of shampoo
• shampoo refill

This is a very common noun-linking pattern in Japanese:

• お茶のボトル = bottle of tea / tea bottle
• 車のドア = car door
• 英語の本 = English book

So here:

• シャンプーの詰め替え = refill packs for shampoo

詰め替え comes from the verb 詰め替える, which means to refill or to transfer contents into another container.

As a noun, 詰め替え often refers to:

• a refill
• a refill pouch
• replacement contents sold without the full bottle

This is very common in Japan for products like:

• shampoo
• soap
• detergent

For example:

• 洗剤の詰め替え = detergent refill
• 詰め替え用 = for refill / refill-use

So in stores, 詰め替え often means the cheaper eco-friendly refill package rather than the original bottle.

も means also or too.

Here it shows that this is an additional good point:

• everyday goods are cheap
• and also they have lots of shampoo refills

So:

• シャンプーの詰め替えも = shampoo refill packs too / also shampoo refills

It pairs nicely with うえに, because both are adding information.

A useful grammar point: も often replaces another particle rather than being added after it.

For example, the underlying idea is something like:

• シャンプーの詰め替えがたくさん置いてあります
• with も, this becomes:
• シャンプーの詰め替えもたくさん置いてあります

So も is functioning where が might otherwise appear.

置いてあります means something like:

• are placed
• are stocked
• have been put out
• are available on the shelves

This form is very common when talking about the state resulting from someone’s action.

Breakdown:

• 置く = to place / put
• 置いてある = to be in a state of having been placed there

So シャンプーの詰め替えもたくさん置いてあります suggests:

• the store has intentionally put many refill packs on display / in stock

Why not the other options?

• あります just means there are
  • more neutral existence
• 置いています focuses more on the action/habit of placing
  • can sound like the store is actively putting them there
• 置いてあります focuses on the resulting state
  • they are placed there and available

In a store context, 置いてあります is very natural because it suggests stocked availability.

たくさん means a lot / many.

Here it modifies the idea of how many shampoo refills are stocked:

• シャンプーの詰め替えもたくさん置いてあります
• They also have lots of shampoo refills stocked

In Japanese, adverb-like words such as たくさん often come before the verb phrase.

You may also see slightly different word order in other sentences, but this placement is very natural.

Compare:

• 本がたくさんあります。 = There are a lot of books.
• 商品をたくさん売っています。 = They sell a lot of products.

So here, たくさん is telling you the quantity of refill packs being kept in stock.

The thing being stocked is シャンプーの詰め替え.

Japanese often leaves out elements that are obvious from context. Here, the sentence does not need to repeat the subject explicitly because it is already clear.

You can understand it roughly as:

• シャンプーの詰め替えもたくさん置いてあります
• As for shampoo refills too, many are stocked

If you made the structure more explicit, it would be close to:

• シャンプーの詰め替えがたくさん置いてあります

But in the actual sentence, も replaces that role and adds the meaning of also.

No. It is saying that the everyday goods at this store are cheap.

That difference comes from the structure:

• この店は = as for this store
• 日用品が安い = everyday goods are cheap

So the store is the topic, not the thing directly described as cheap.

If Japanese wanted to say this store is cheap, that would sound odd in English too, but grammatically it would be something more like:

• この店は安い
  which would usually be interpreted in context as things at this store are cheap, not literally the building or store itself.

In your sentence, the inclusion of 日用品が makes it very clear that the cheap thing is the everyday goods.

Yes, in natural English that is often a very good translation.

Literally, it is closer to:

• many are placed / stocked

But when talking about a store, natural English often prefers:

• they carry a lot of shampoo refills
• they stock lots of shampoo refills
• they have plenty of shampoo refill packs

So while the Japanese wording focuses on the state of items being placed in the store, the natural English translation often uses carry, stock, or have.