Part 1: Okay, so, considering the fact that ‘XYZ’ brand is related to your blog’s niche, you have a good probability that your pitch will be successful. If your blog is about “Security” and stuff, then if you approach an Antivirus brand for a sponsored/paid review, then, yes, it’s possible that they might like your proposal.
Part 2: I would suggest you have an email address like firstname.lastname@example.org, where ‘name’ is your first name, and ‘example.com’ is your blog’s address. This is the key step to look official first.
Part 3: Now, what you have to do is, email a brand which is into security and software field, do their review for free, yes, free. Make it exclusive and detailed. Get good social shares and comments for that post. After this, get that brand’s testimonial, like saying, how your review helped them to get good exposure or sales if it’s true.
Part 4: Now, you need to pitch your real advertiser, that ‘XYZ’ antivirus brand. Pitch them saying (in a professional way) about your blog’s current authority and traffic. Your social media influence and engagements. Then, at the end, mention the previous free review (don’t mention it as ‘free’) and tell them how you helped that brand to get more exposure and sales. That’s all.
Forget the money part, once you convince them, you can pitch a good amount according to the brand’s value and your blog’s value. Best wishes.