The 2 important metrics are Bounce rate and CTR. These are based on on-site SEO and most users don't even try to optimize their site for this. They just go on for link building which can, no doubt, give them ranking. But would you really be happy being on number three and making less sales than the site at number 5.
I have personally experience this with one of my eCommerce site. I checked the SEO reports in Google analytics and always analyze the CTR and landing page. What you want to check is see which pages are getting more CTR for a given search keyword (you have to analyze each of your keyword manually). And if it is not the main page/product page, but an inner page that you don't want to rank for that keyword, its natural that a visitor to that page will just exit (considering that it is not the page that you want the visitor to land for the given keyword, this results in high bounce rate).
So now you know which inner page is ranking for a keyword that it shouldn't be. Just write up a content and description similar to it for your main page (that you want to rank for this keyword). Within some days Google will crawl and update the changes and you are more likely to see the new changes you did as search snippet. Now with the same search engine position and no external backlinks build, you just increased your CTR and reduce your bounce rate by landing the visitor to a useful page.
Note: This is not a one off process. Google does not show search snippets according to you, so you have to monitor those thing and make regular small changes until your search snippet gets as closer as possible to the highest CTR page. Don't just copy the content and description from that page, unless you want penalty for duplicate content. Just create similar content with the keywords.
Result: Even without creating backlinks, I improved my site CTR and bounce rate considerably from around 70% to below 58%. And Google liked high CTR and low bounce rate, so my site got pushed up considerably in SERPs without much baclinks (considering the top has around 10K backlinks, and mine still under 500).
Conclusion: I fear your colleague is right. At the end of the day your client wants to get more sales and not just ranking (quality traffic).
OR your colleague may be talking of PPC, paid campaigns. OR he has completely gone mad.