Links and content are important but I think far above this now is trust. The best way to get trust is SSL the whole site, get reviews on big review sites, and listed in DMOZ. 2 cents....
I think its an old one because back then until now we must gain first the trust from the target audience so that we will be established from the respected niche.
Some old stuff still valid. For example content still plays major role. Trust is important. Google has a concept called "E-A-T". T stands for trust. SSL is one method to improve trust. Also online review systems will also help to improve trust.
You can't gain trust with crappy content and trust is gained/shown through links, so they're all necessary. SSL is for security and data, if this was the case for trust everyone could just add an SSL. Google has said adding an SSL will only give you a slight advantage over your non-SSL competitors with everything else being equal. So unless you're in a really competitive niche and every rank position counted, I wouldn't even bother with it (unless you take payments online/sensitive info/real business). You might as well forget about DMOZ. The "trust" that everyone refers to is from actual sites. Example FB/Wikipedia/Twitter/CNN/Google/Yahoo/WSJ/Huffington Post/CBS/LinkedIn/etc sites like these have major trust therefore acquiring a link from one would increase your site's trust. The more links from these kind of sites the more Google trust you. Brandnewsite(.)com would have zero trust. Majestic(.)com are the folks that came out with the trust metric.