Is this considered black hat

I don't know if search engines are particularly identifying that sort of thing but I think it's definitely unethical. The sites you are writing reviews for would definitely care and could ban you if they find out. I imagine they would be on the lookout for this sort of thing.

Although, this could be identified by SE's as a potentially self-created link and devalued. I know they have some interest in self-created links but I have no idea if product reviews would be included in that.

Definitely not hard core blackhat, I think your technique falls under the spammish category. Unless your posting those reviews on a site already indexed by the SEs that has some authority, I think it would be a waste of time, not to mention unethical.

Why don't you just buy some "real" reviews (reviewme.com, text-link-ads.com/post_level/, payperpost.com/)? It's a tad bit more ethical, and you would get backlinks from sites that are already indexed by search engines that have a little bit of authority. If you can't afford that, just make your page convert well, and do some PPC. And because your site is commercial, it's going to have a tougher time getting ranked in Google. Informational sites do much better in the SERPs.

If you are just going to create another site on a new domain, and just review your products and link to your own product pages, it's going to be a waste. I think Googlebot could figure out that your review site, and your shopping site are in it together. I don't know how it will affect your rank, but I'm sure Google will loose trust in your sites, which will hurt you in the long run.

If you decide to pay for reviews like I suggested, make sure you don't just have the reviewers link to your homepage. Make sure to spread the link love by making them link to subpages, else it looks unnatural.

The site filled with reviews only and having lots of links to your site will be considered a doorway and banned.

I think they might notice if a lot of links appear from similar sites appear in a very short amount of time. That's something they do keep track of - the distribution of links over time.

I would take a step back and be asking... "why is your site so difficult to listed"?

Code, products, site build? If it's a well built, SEO site than getting listed shouldn't be a problem. If they have an extensive product line why not write tips to go along with each product, build more pages and get people interested that way.

post on review site as teammatt suggested and get some good links from directories within your industry, should do the trick.

Cheers, Chris.

You mean your site has not yet been indexed? Try building links for your site would be cached faster