A tourism boss wants clearer government advice on people travelling from areas with England's highest level of coronavirus restrictions.
Sally Everton, from Visit Devon, said they had to rely on people sticking to guidance that they should not travel.
"Those areas are in lockdown and I'm trying to believe those people will remain in lockdown," she said.
A holiday park owner said he had cancelled bookings made by people from tier three areas.
Ms Everton said tourism businesses were on a "knife edge" and she was concentrating on encouraging local tourism for day trips.
Malcolm Bell, chief executive of Visit Cornwall, urged all his members to call guests in advance to find out where they are from.
He said it was "easier to have that conversation" before people travelled down and he hoped those conversations would lead to people rebooking or maybe being refunded.
Liverpool City Region and Lancashire are currently under "very high" tier three measures, with Greater Manchester joining them from Friday and South Yorkshire from Saturday.
The government advice for people in tier three areas states: "You should avoid staying overnight in another part of the UK if you are resident in a very high alert level area, or avoid staying overnight in a very high alert level area if you are resident elsewhere."
John Hyatt, the director at Hendra Holiday Park near Newquay, which has cancelled bookings, said he was surprised people from tier three areas had only been given guidelines, not restrictions.
He said: "We made contact with those guests from tier three and relocated their booking or gave them a refund."
Carolyn Armstrong, who owns the Headland Hotel in Newquay, said the hotel was "extraordinarily busy still".
She said: "We can certainly all look up the addresses of people who have made bookings but it is going to be jolly tricky because if they have got a contract and they are allowed to travel legally then they can travel."