Conversion fee charges - do sellers need to indicate these clearly?

[DojaPhat]

Hoping someone can shed some light on this - if you buy something on a website which was ostensibly advertised in pounds sterling but ended up being charged a conversion fee because the company operate in dollars, is this just unfortunate because some banks wouldn't have charged the conversion fee or is there any onus on the seller / website to clearly indicate the associated fees/conversion regardless?

If it's priced in pounds I'd expect to pay in pounds not dollars and then have my bank convert. If you do stuff in foreign currency often it's worth looking for a card that has no conversion fee (for example Santander Zero if still available).

Or one of the pre loaded cards often used by holidaymakers.

If it is your bank or credit card provider that is charging the conversion fee, the website has no way of knowing if such a fee will be charged or how much it might be. If that is the situation, there is no onus on the seller to indicate the associated fees as they are not their fees.

Thank you both! If I'd taken some notice I could have used a card with no fees but all sorted now.