Booking a ferry should take ten minutes. Often it does — and then you spend another twenty untangling a booking fee you didn't expect, a name that doesn't match a passport, or a ticket that can't be moved. Most of the problems readers write to us about come down to a handful of avoidable slips at the checkout stage.

None of them need expert knowledge to dodge. They mainly need you to slow down at the moment the site is nudging you towards the "Confirm and pay" button. Here are the ten that catch people out most often, and what to do instead.

1. Comparing the headline fare instead of the final total

Ferry pricing is modular. The price you see in the search results is usually the base fare for one vehicle and a set number of passengers, before anything else is added. By the time you reach the payment page, the number can look quite different.

Watch for these extras, which are often pre-selected or easy to miss:

• Booking or administration fees added at the last step
• Card surcharges, or a fee for certain payment methods
• A "flexible ticket" or cancellation cover box that is already ticked
• Reserved seating, priority boarding or cabin upgrades
• Extra passengers or a larger vehicle class than you selected
• Text message confirmations, pet supplements or trailer charges

Do your comparisons at the payment page, not at the search results. Compare like with like: same route, same sailing time, same vehicle, same number of people. If a price seems unusually low, the reason is usually on the next screen.

2. Choosing a non-refundable fare without realising it

Most operators now sell two or three fare tiers on the same sailing. The cheapest is usually the least flexible. It may be non-refundable, or refundable only as a credit, or amendable only if you pay a fee plus the difference in fare on the new sailing.

That is not a scam — it is how the cheaper seats are funded. The mistake is buying it by default and then assuming you can move it later. Before you choose, ask yourself:

• What happens if my plans change by a day, or by a week?
• Can I change the passenger name, and at what cost?
• What is the deadline for amending, and is it before departure or before check-in?

If the crossing is a small part of a bigger, more expensive trip, the flexible fare is often worth the difference. If real money is at stake, read the cancellation terms before you pay, and take professional advice if the wording is unclear.

3. Passenger details that don't match your passport

Names are checked against travel documents on many routes, so book the name exactly as it appears on the passport — including middle names if the booking form asks for them. "Dave" on the ticket and "David" in the passport is a classic source of friction at the port.

Two other details get overlooked. First, the lead passenger's email and mobile number: this is how operators send timetable changes, weather disruption notices and boarding instructions. A mistyped address means you hear nothing. Second, children and infants usually need their own entry with a date of birth, and some routes price them differently, so don't lump them into an adult count.

4. Getting the vehicle wrong — length, height and extras

Vehicle categories are not just about cars versus vans. They are about size. If your car is longer than the category you booked, or you arrive with a roof box, a tow-bar bike rack, a trailer or a caravan that you didn't declare, you may be charged the difference at the port or refused boarding on a full sailing.

Measure properly rather than guessing, and check the small print for what counts as part of the vehicle. Over-declaring is the safer error: you pay a little more, but you avoid an argument at the check-in booth when the sailing is busy.

5. Booking the wrong port, terminal or date format

Ports with similar names catch people out constantly, and larger ports such as Portsmouth, Dover and Calais have multiple terminals or berths. Save the full address and postcode for the terminal on your confirmation, not the port town, and check which operator you are sailing with — two companies can leave the same port from different entrances.

One more trap for anyone booking on an overseas website: date formats. A booking made as 03/04 can mean March or April depending on the site's convention. Read the confirmation back carefully and check the day of the week matches the date you intended.

6. Assuming the check-in window is flexible

Check-in deadlines vary by route, operator and season, and they are usually an hour or more for vehicles on routes with border checks. Boarding closes before departure, not at it. Turn up late and your ticket can be treated as a no-show, even if the ship is still at the berth.

In peak summer, queues at the port are the real risk, not the sea crossing. Build in spare time, especially with a long drive beforehand, and if you are catching a train or flight at the other end, don't book the tightest possible connection — allow for delays and for the fact that some sailings do run behind schedule.

7. Forgetting luggage, pets and accessibility arrangements

Some routes include generous luggage allowances; on others, particularly fast craft and certain foot-passenger services, there are limits on bags and bicycles. Bike spaces in particular are finite and often need reserving in advance.

If you are travelling with a pet, check the current requirements with the operator and the relevant government authority before you book, as rules and paperwork requirements for bringing animals into and out of the UK have changed in recent years. For assistance dogs, notify the operator when booking rather than on the day.

Passengers needing step-free access, a lift, or help boarding should request assistance at the time of booking wherever possible, and confirm it in writing. Ferry terminals and ships vary enormously in how accessible they are.

A five-minute check before you pay

1. Read the total price on the payment page, with every add-on included.
2. Check each passenger's name against their passport, letter for letter.
3. Confirm the vehicle category, length and any roof box, rack or trailer.
4. Check the port, the terminal, the postcode and the exact sailing time.
5. Re-read the amendment and cancellation terms for the fare you have chosen.
6. Save the confirmation as a PDF and add the check-in deadline to your calendar.

Do those six things and you will avoid almost every problem that lands in an inbox the night before a sailing. Take a screenshot of the confirmation too — it is handy when port Wi-Fi inevitably lets you down.

Photo: KAMcMillan / Pixabay