Not at all, the only reason a company will come after you is if you source their product through an unauthorised distributor.
For example, if you have a friend passing you Louis Vitton bags out the back door at their distribution centre, then you are not an authorised seller and they won't be happy.
Of course not all brands are tightly controlled through such authorised networks, that is mostly designer type branded products, it was just an example.
Depending on what you are selling, you will most likely be able to buy in from a wholesaler or even factory direct depending on your line of credit.
So long as you are buying form an authorised source, and not selling fakes, which you wouldn't be anyway if you are buying from a legit source, then there are no issues at all!