There are so many different parameters and issues to your question that if you really want to pursue it you should be consulting with competent local legal counsel and not trying to get answers for free online; DIY in an area such as this is really not a good idea.
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Yes it can, especially when as described in your post one is comparing apples to oranges.
No, you have no short term options to stop it, other than not buying your products there - vote with your feet!
Disclaimer Information on this site is provided by Brian Scott Wayson as general information, not legal advice, and use of this information does not establish an attorney-client relationship. If you have questions about your specific situation, please call an attorney.