It was clear they had arrived from the airport, she said, and told her they had booked the house through Booking.com.
After Gillian told the tourists she didn't rent the house out, the travellers "looked aghast".
Unfortunately, this wasn't the only time it happened. Later that day, more travellers showed up and also believed they had also booked the accommodation.
On July 5, Gillian contacted the website to request the listing be removed. Six days later it was pulled from Booking.com but she still had around 23 groups of tourists show up to her house, totalling around 100 people.
"They came from all over the world. Australians who'd just arrived, there were some people from Saudi Arabia, some people from the north of England, and I just couldn't believe it," Gillian said.
Unable to offer any rooms, she could only tell them it was a scam and send them away.
"They're very nice people, but perhaps one day we might get some people knocking on the door who actually are quite aggressive. I feel very vulnerable."
According to a Booking.com spokesperson, the company took safety and security "very seriously" and most of the millions of experiences every week had "absolutely no problems".
"Scams are unfortunately a battle many industries are facing against unscrupulous fraudsters looking to take advantage and it is something we are tackling head on," they added.
Booking.com claimed travellers caught out by the London scam were contacted and provided refunds, relocations and help with additional fees.