Making eye contact has long been held as an essential tool of the hand-selling game, creating a bond with customers and engendering feelings of trust and empathy.
But it can also be a useful weapon in the battle against under-age drinkers.
New research from Serve Legal - the commercial organisation that carries out test purchases of alcohol using young people of legal drinking age - shows that making eye contact increases the chances that staff will feel comfortable in challenging the customer and asking for ID.
In turn, that reduces the overall risk of making an illegal sale on those occasions when real customers may be under-age, and putting the future of the business in jeopardy.
In a study of 144,620 visits made by Serve Legal test purchasers to stores in 2008, 61% made successful challenges when eye contact was made before the transaction took place, compared with just 49% doing so during the transaction.
Where no eye contact was made at all the pass rate was just 4%.
Displaying point-of-sale material can also have a positive effect on pass rates, constantly keeping the store's Challenge 21 or 25 policy front-of-mind.
One retailer used by Serve Legal to test out its procedures saw sales increase from 41% in outlets without point-of-sale to 54% in those that did have it.
For legal reasons, Serve Legal can only use young people aged 18 or over for its test purchases, which it carries out on behalf of retailers and pub groups
to check that their own policies and
procedures are being followed by staff.
The overall pass rate - meaning that ID was asked for during a transaction - rose from 55% in 2007 to 66% last year on the 14,620 occasions that Serve Legal
conducted test purchases.
The off-trade consistently outperformed the on-trade, scoring 66% versus 54%, which Serve Legal director Charlie Mowat said was largely because of a greater level of engagement with the issue in take-home.
"The on-trade is struggling much more financially and just doesn't have the same level of funding to spend on this sort of thing," he said.
C-stores lift their game
Convenience stores raised their game in 2008, increasing their pass rate from 62% in 2007 to 66%, and closing the gap on supermarkets - down from 69% to 67% - to just one point, from seven a year earlier.
"We had a lot of convenience stores start working with us in 2008," said Mowat.
"Independent stores are becoming more aware of the issue and of the consequences that could come from failing a test purchase if it was carried out
by trading standards or the police."
There were big regional differences in pass rates, with southern England, London and Scotland doing best, and Wales and Northern Ireland less well.
"It's difficult for retailers because of the inconsistency of approach across local authorities," said Mowat. "It's very difficult to have a consistent performance across the company when there isn't a consistent approach from the authorities across the country."
But Mowat did add that the power given to Scottish trading standards officers to carry out their own stings had a significant impact on shops' performance in 2008, even though the powers had only been used sparingly so far. Scotland's Serve Legal pass rate increased from 57% in 2007 to 68% in 2008.
The level of supervision within individual stores can also impact on ID-checking performance, with lower pass rates on Sundays, compared with other days of the week. Mowat said this was down to
the combined effects of more casual staff working and managers taking days off.
But he said there was no evidence to support a popularly-held view that checking for ID goes out of the window when a store is busy.
"It can be quite the opposite," Mowat said. "Sometimes the pass rates drop down when you wouldn't expect it to be too busy, such as early in the morning, which may just be because the staff aren't as switched on as they are when it's really busy."
The general move to Challenge 25 from Challenge 21 policies in the industry is likely to have a positive impact, according to Mowat.
Proof's in the results
One Serve Legal client that rolled out Challenge 25 in 2008 saw an increase in their pass rate from 79% to 85%, and the signs were such an improvement
they were being repeated in other retailers.
"With Think 21 or Challenge 21, the judgement that staff tend to be making is still whether someone is old enough to buy alcohol or not, but there's a mental shift with Think 25 towards staff asking themselves: 'Are they young enough for me to have to ask for ID to make sure?'"
While the report shows a positive shift in retailer approaches to ID - especially in the off-trade - there's still room for improvement, said Mowat, and the
recess ion could yet have an impact.
"Getting to 100% is going to be incredibly difficult, but we do have retailers who are aiming for that.
"The recession may mean that more companies start to cut back on the overall spend on this issue and there's a risk we could see the improvement fall back. But it is only a risk rather than something we're seeing happen so far."
Mowat's hope is that companies continue to invest in training on ID issues.
"Training works best if it has an interactive element, and it can also help to try to understand how staff feel when they're having to make those challenges. What is going through their mind?
"Getting together in a group and going through some photos of young people, trying to work out their ages, can be much more effective than just someone telling the staff what to do."
But when you do, don't forget to tell them to make eye contact.
Key Serve Legal 2008 report findings
Total on and off-trade test purchase pass rate 66% (2007:55%)
Total off-trade test purchase pass rate 66%
Total on-trade test purchase pass rate
Supermarket test purchase pass rate 67% (2007:69%)
Convenience store test purchase pass rate 66% (2007:62%)
Pass rate where test purchaser is male 67%
Pass rate where test purchaser is female
Highest regional pass rate, South Central England
Worst regional pass rate, Northern Ireland 56%