If you are going to use that car then you definitely need to do something other than a white box on the tag. Either photoshop it out or blur it or something other than a box. That doesn't look professional at all. It looks like you made your business cards yourself instead of having them professionally done and you should really try to avoid that impression even if its true.
From a graphic design standpoint the black text box on the front isn't the best idea either. There are other ways of making that a little easier on the eye. You have soft colors and smooth angles in the background and on the car and then WHAM! you've got this big black box on the side. Again, it just goes to the professional look of the card.
On the back I only have a couple comments. I don't thing the use of "European Botique" products is necessarily bad, but I would probably drop the term Boutique. That has a different connotation to different people. Around here a Boutique is where we get our porn and sex toys. I'm not trying to be crude, but it's just because that is the name of the store and everybody knows it. Everytime I see the word I think of perverts or The Fuzz.

(he's gonna have to read a lot before he sees I said that about him) Knowing the real definition of Boutique I still think of products with that term attached to them being products that aren't good enough to sell in the main stream so they end up getting sold at little hole in the wall locations in crappy malls. Anyway, that is my rant on 'boutique'.
I wouldn't say they are enthusiast grade products either. They are looking for a professional and since you are one then they should know you are using professional grade products. Just because you can't buy something in gallons or barrels doesn't mean it isn't professional grade. Don't underestimate the quality of what you are using. I do like that it implies that 'enthusiasts' (who are usually the most anal about what products they use) have a higher standard for their products, but only an enthusiast would understand that. If that is the point you are trying to make then there are probably other ways you could word it.
The font doesn't do much for me on the back either. Kinda hard on the eyes. I prefer a nice Verdana or High Tower font on things like that.
Those are just my nitpicks. Overall I really like the layout of the card. The colors on the front are great and that is a great eye catching picture. I like the information that is on the back and how it is laid out. I only suggest a couple graphic tweaks on the front and some verbiage changes on the back and it would be a sweet card. That is much better than any of my efforts ever turned out. Now I just go to VistaPrint.com and have them make cards for me. Very good work on your part though. I look forward to seeing the final product.