A friendly customer service agent and short wait times can pay off in a big way for sales-based call centers, according to “America’s Call Centers Revealed,” a new study from the Marchex Institute, the research arm for mobile advertising analytics company Marchex.

Marchex Institute researchers analyzed the outcomes of more than 21 million calls to businesses across a wide variety of industries and learned that the simple things–such as a “warm greeting” from a customer service rep–can lead to millions of dollars in potential sales.

“Consumer phone calls that resulted in a purchase were answered with a warm greeting 63% of the time, compared with 41% of calls that did not result in a purchase. For a large call center, a warm greeting can equate to $20 million in additional revenue annually,” the Marchex researchers wrote.

“We have all heard that being nice to your customer is good for business,” said John Busby, Marchex’s senior vice president of Marketing and Consumer Insights. “This study clearly shows that putting the golden rule to work inside a call center can truly turn into gold for that business.”

The study also revealed consumers’ tolerance–or lack thereof–for being put on hold when reaching out to a call center. Fifty percent of callers who hang up after being put on hold do so within the first three minutes.

Another thorn in the side of customers is the ubiquitous IVR, or interactive voice response, system. The IVR is often the first form of contact between a consumer and a call center. According to Marchex, 11% of most industries’ customers will hang up during interaction with an IVR system. It’s worse in the cable industry, where 14% abandon IVR (62% of callers dump the IVR within a minute).