When can a blogger ask for sponsorship?

I started beauty blogging four years ago. My blog ran on nothing but my time, computer, internet connection, and a student's allowance. Starting out I wrote general information articles on beauty and reviews on products I buy. Four years later, I am earning quite a good sum of my money from my blog alone. The swag I get every month is maybe worth five figures. And I still write general information articles and reviews on products. :)

I sound like a bragging asshole just about now but I'm telling you this because my "success story" is not as simple as it sounds. For the past four years I invested a huge chunk of my time and money on this website. Waking up at 6am just to write and process photos, planning my content days beforehand, marketing my blog and personal brand, these things are not a walk in the park. I have what I have because I'm passionate about my niche. I did this when I got nothing out of it. I will still do this even if all my sponsors leave me.

My actual job is handling the social media and PR of retail brands. Every so often, a new blogger messages or emails these brands asking for "sponsorship". That is, free stuff for their blog review or contest.