Is it haram to buy things without paying customs duty?

What counts as dodging customs?

• Walking through the "nothing to declare" lane with goods over your allowance.
• Asking an online seller to mark a parcel as a "gift" or lower its value.
• Splitting an order into small parcels just to stay under the limit when the rules forbid it.
• Bringing items in for resale while claiming they're for personal use.

Each of these involves a false statement, and the Prophet ﷺ said, "Whoever cheats us is not one of us" (Sahih Muslim 101). Lying to save a few pounds or dollars is still lying. See Is it haram to lie on government forms?

Keeping trusts and agreements

When you enter a country, you accept its rules on what you bring in. Islam asks Muslims to honour such agreements and give each party what it is owed:

Customs duties fund public services and protect local businesses, much like other taxes. See Do Muslims have to pay taxes?

Didn't scholars criticise "maks"?

Classical scholars strongly condemned "maks," unjust tolls that rulers took from traders. A few modern writers use this to argue that all customs are unjust and can be avoided. Most contemporary scholars and fiqh councils disagree: duties set by law in a country you've chosen to live in or visit, and used for public services, are not the same as arbitrary extortion. Even someone who personally thinks a duty is unfair still isn't allowed to lie to avoid it; they can campaign to change it instead.

What's fine

• Using your full duty-free and personal allowances.
• Choosing sellers that include duties honestly in the price.
• Claiming VAT refunds or reliefs you're entitled to.
• Asking customs staff what applies before you travel.

If you've avoided duty in the past, repent and, where you reasonably can, pay what you owe. Honest travel is part of good Islamic manners. See What are the Islamic manners of traveling?