Подделку нельзя перепродать.

Because it is the direct object of перепродать (to resell).

The base noun is подделка. Its singular forms are:

• nominative: подделка
• accusative: подделку

In this sentence, the thing being resold is the fake/counterfeit item, so Russian uses the accusative:

• Подделку нельзя перепродать.
  = A fake/counterfeit item cannot be resold.

Russian often uses impersonal constructions, especially with words like нельзя.

Here, the sentence does not explicitly say who cannot resell it. The idea is more general:

• It is impossible to resell a fake
• A fake must not be resold
• You can’t resell a fake

English usually wants some kind of subject like you, one, or it, but Russian can leave that out naturally.

Нельзя is a very common impersonal word meaning something like:

• it is impossible
• it is not allowed
• one must not
• you can’t

Its exact meaning depends on context.

So Подделку нельзя перепродать can mean either:

• It is impossible to resell a fake, or
• A fake may not / must not be resold

Without more context, both are possible. In real usage, нельзя often has a strong sense of not allowed.

After нельзя, Russian normally uses an infinitive:

• нельзя курить = smoking is not allowed / you must not smoke
• нельзя войти = it is impossible / not allowed to enter
• нельзя перепродать = it is impossible / not allowed to resell

So the pattern is:

• [object] + нельзя + infinitive

Here:

• Подделку нельзя перепродать.

• продать = to sell
• перепродать = to resell, to sell on

The prefix пере- often adds the idea of again or onward.

So:

• продать подделку = to sell a fake
• перепродать подделку = to resell a fake

That means the item has already been sold or acquired once, and now someone wants to sell it again.

Перепродать is perfective, while перепродавать is imperfective.

• перепродать = to resell, viewed as a completed whole action
• перепродавать = to be reselling / to resell repeatedly or as a process

After нельзя, both aspects are possible in some contexts, but they give different shades of meaning.

Here, перепродать suggests:

• the act of reselling is not possible / not allowed as a complete act

If you said Подделку нельзя перепродавать, it would sound more like:

• A fake must not be resold in general
• One must not engage in reselling a fake

So the perfective version is natural if the focus is on the single act being blocked.

Russian word order is more flexible than English word order. Putting подделку first makes it the topic or point of focus.

• Подделку нельзя перепродать.
  Focuses on the fake/counterfeit item
• Нельзя перепродать подделку.
  More neutral: It is impossible/not allowed to resell a fake

Both are grammatical. The first version may feel slightly more emphatic, as if answering a question like:

• What can’t be resold?
• A fake can’t be resold.

No.

• подделка = a fake, a forgery, a counterfeit item
  This is a thing
• подделывание = forging, counterfeiting, the act of faking
  This is an action/process

So in this sentence, подделку refers to the object itself, not the act of making it.

Yes. That is a very natural English translation.

Because Russian often leaves the subject unstated in impersonal sentences, English may translate it in several ways:

• A fake cannot be resold
• You can’t resell a fake
• A fake must not be resold

Which one sounds best depends on context and on whether the meaning is more about impossibility or prohibition.

The usual stresses are:

• подде́лку
• нельзя́
• перепрода́ть

So the full sentence is pronounced:

• подде́лку нельзя́ перепрода́ть

Stress is important in Russian because it is not always predictable from spelling.

Yes. If the object is already known from context, Russian could use a pronoun:

• Её нельзя перепродать. = It/Her cannot be resold

But in practice, using её could be ambiguous, because it might refer to any feminine noun.
Using подделку is clearer and more specific.

It is basically neutral Russian.

All three words are standard and common:

• подделка = standard vocabulary
• нельзя = very common
• перепродать = standard verb

So the sentence could appear in everyday speech, legal discussion, business context, or warnings, depending on the situation.