Cheaper look-alikes have been around for years, but social media has made them more popular. Dupes can move into shaky legal territory if concerns arise around consumer confusion or patented designs.

Lululemon alleges that Costco has stolen the intellectual property of its Scuba hoodies and sweatshirts, Define jackets and ABC pants.

Lululemon is accusing Costco of stealing from its "path-breaking" brand by selling dupes of its sweatshirts, jackets and pants.