Ever walked into a shop, thought "I've seen that cheaper online" or even tried to find it cheaper online?
The practice is known as "showrooming" and research by mobile phone operator EE shows that half of UK consumers now use their mobile device to browse for better deals while out shopping – even before they have left the premises.
According to the research, 44% of consumers – more than 20 million Britons – now visit a physical store while browsing products online in the hope of finding a better deal.
Almost 80% said they prefer to browse product ranges online, and 88% said they think they are more likely to find a good deal by looking online as opposed to visiting the store.
The younger generation of shoppers – those aged between 18 and 34 – were the most prolific users of devices while in store, according to the poll.
Often shoppers even try clothes or shoes on for size before leaving the shop empty-handed – only to have the item delivered to their homes via the internet.
And it's understandable that retailers are becoming more and more concerned about "showrooming".
The amount of money spent online broke the £10bn barrier for the first time at the end of 2013, a 10% increase on the previous year.
Meanwhile, retail on the high street fell by nearly 3% in the same period.
Another poll by design agency Foolproof in April found that 24% of people showroomed while Christmas shopping – and 40% of them took their business elsewhere.
According to researchers at market research company TNS, one third of consumers around the world admit to the tactic.
And a survey from Omnico last year said that 39% of Belfast shoppers admitted to "showrooming", one of the highest percentages in the UK.
While some retailers try to stop it by ignoring consumers' desire for free wifi or even blocking mobile signals, others are offering assisted selling and integrating their mobile and web channels.
EE is allowing canny companies like John Lewis to cash in with its Connected Retail service, which enables staff to connect to customers as they shop.