Depending where you are in the world, but in the US, yes anything that replicates someone else's work is considered copyright infringement. I believe there is a set rule for variation, which is 30%, if i recall to not be considered as infringement. Do your research first and as stated, I also am not a lawyer.
Personally I would look at it as copyright infringement because you are technically copying someone else's design/layout. Plus viewers/buyers may consider it shady that your are similar to someone else and not creating your own work. Also, wouldnt you be annoyed if you found someone else doing similar work, site designs, or selling tactics as you?
Good read, THE IDEA-EXPRESSION DICHOTOMY IN COPYRIGHT LAW
What is copyright infringement?
Copyright infringement occurs when someone other than the copyright
holder copies the “expression” of a work. This means that the idea or
information behind the work is not protected, but how the idea is
expressed is protected. For example, there have been many movies about
Pirates, but only one Jack Sparrow.
Taken from Click and Copyright