If it is luck it will even out in the long run. Hopefully you will get to stay that long.
However, from someone that has been in sales (not car), there are significant factors other than luck that will vary your longterm sellrate. Granted, selling a car is probably more difficult than selling someone a service plan at Best Buy. However, I would imagine that selling add-ons are very similar.
I don't know what kind training you've had or if you have a sales background, but you could also have significant leaks in your game. Things like overcomming objections and building a solid raport with your customer will impact your results significantly. Try to know common objections and have rebuttals ready. You must believe in your product and make sure your customer sees this. If you don't (or at least aren't very good at appearing that you do), it will me much more difficult to sell.
Try different ways of selling, see what works for you. Change your delivery, timing, phrasing, etc. It's certainly difficult to find what's the best, but once you figure it out it will be the difference between when you read your first poker book and when you started crushing 8 tables whatever limit you play for 3bb/100.
That said, I don't really miss my sales days. Although the feeling you get when you close a tough sale, I miss. (especially when someone else couldn't seal the deal.
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-Craig