I know someone who trained their pet with treats, and now the pet will only do what it’s asked if it knows there is food available.

This is a problem that can occur if one doesn't wean away from having food in the hand and doesn't move to the random reward schedule mentioned in the previous Q&A. It isn't a flaw in the training method, but a mistake in how the methods were implemented.

I will work with you to establish behaviors using rewards, and then show you how to transition away from using rewards for every repetition so that your pet will respond to you happily without the promise of treats or other immediate rewards.