There can be few more depressing office sights than the salesman who can't sell. They ooze failure and reek of rejection. An instinctive reaction is to shout at them, or sack them. But employers frustrated by poor sales performance might first consider whether they themselves might be to blame.

Your typical sales person may have everything they need to do their job well, says Russell Ward, chief executive of sales training company Silent Edge. "They look good, have great personalities, are capable of establishing a rapport with prospects and have good knowledge of the products and services they are offering," he says. "But-and it's a pretty big but-they're not as good as they could be at selling."

Ward's company has done a benchmarking study of sales teams at blue-chip businesses and found that only one in five deals ever gets closed. Vast tracts of sales and marketing resources are being wasted, he says.

That's because, according to the study, sales staff are often weak in key areas, such as closing deals, handling objections and negotiating offers. But should they be blamed? "In most of the cases we've seen, it's actually more the fault of the training process than individual incompetence," says Ward. "We seem to labour under the delusion that great salespeople are born, not made."

Companies in Ward's study didn't do enough to train sales staff and were bad at managing them. Most sales managers get the job because they were a successful sales person. "The problem is, the qualities you need to be a successful sales manager are often the antithesis of those that make a successful sales person," says Ward. For one, they have to focus on what the team as a whole is doing, and not just on their own sales record.

Valerie Heritage, a sales expert at the Communication Challenge, believes sales staff need leadership and encouragement, but get nowhere near enough of either. Her company researched the issue in conjunction with the Institute of Sales and Marketing Management. Businesses in the study, which included household names such as Barclays Bank and GlaxoSmithKline, were "fixated on the bottom line" and put too much emphasis on short-term performance.

Heritage believes senior staff should spend more time coaching junior employees-giving them feedback and advice on how to improve. At one of the companies in her study, senior sales staff each spent 120 days a year on coaching.

Bob Etherington, an expert salesman and author of Cold Calling for Chickens, also stresses the need for coaching and encouragement. Selling is a journey of small, incremental steps, he says, and to be successful "you've got to plan it like a military campaign".

Constantly asking sales staff whether they have closed the deal is hugely demotivating, adds Etherington. "Managers should be involved right from the start, helping the sales staff to set their strategy," he says. "It's very straightforward, but most people don't do it." Perhaps they find it easier to shout and stamp their feet.