People have been buying liquidation pallets for a long time. Yes, even before the internet was birthed this was a process that took place at in-person auctions and events. Nowadays, there are hundreds of places and/or sites that you can purchase liquidation pallets from.
Your job is to learn which wholesalers and products work best for you and then exclusively pursue those opportunities. Just like everything else, this is a lot easier said than done. However, the best teacher is experience and your only option before the experience is to learn from the successes and failures of others.