OP, we foster rescue dogs (from shelters), in addition to owning two now and many over the years, and the PPs are right -- they DO indeed regulate. Every single one of them. Some prefer to pee/poop only when off-leash, in your yard. Others do their business at first only on a leash, no matter how long they are left outside. But all eventually regulate to your routine, if you are CONSISTENT with that routine. Also, it IS possible to train your dog to pee and poop in partiuclar spots. Our current rescues are 11 and 8, the 8 yr old adopted two years ago and the 11 yr old adopted this year, and both were able to be trained easily by my taking them to the SAME place to pee, regularly, the minute we walked outside of my house. I would walk them out, purposefully, and point to a partiuclar spot and say "go pee." At first they would just look at me, but eventually they got the message -- if they didnt' pee then but started to somewhere else, I immediately pulled them to the spot I wanted them - that THIS was where I wanted them to go. No more ruined lawn and no annoyed neighbors - they pee on the side of our yard by the woodchips.
Good luck with your new family member, and I am very glad you risked DCUM wrath to find out never to leave your dog outside the store.
Thanks for asking and not just assuming you know it all