UTD on all shots; likes other dogs, cats and kids, may or may not be house trained. Ooooh; that one might just sink the deal right? Many second hand dogs are not house trained, there are several reasons why they may not be house trained yet.
1. The first owners never bothered to train the dog.
2. The dog lived in a cage, they just eliminated in their cage.
3. Some dogs regress when they are placed into a new home.
4. Often dominant dogs mark new areas, they may have been house trained in their first home but now everything needs marking.
So whatever the reason is that the dog you are interested in is not house trained, there is good news. House training is not one of the difficult issues. Some catch on quicker than others but most can be trained up with some serious structure, consistency, patience, praise and reward.
First line of defense is supervision, I'm a supervision nut. If you don't have your eyes on your dog, how do you know what they are doing? And how can you educate them if you don't know where and what they are doing? You can't, bottom line. So basically you are going back to kindergarten, you have to start back at the very beginning. Even if you have acquired an adult dog you must consider the fact that they do not know that they should not eliminate in your house.
So, this means that you must supervise your dog at all times. If you do not have your eyes on your dog then they need to be in an expen, crate, small room where they will not pee or poop or leashed to you as you move about. The important thing to get started is lowering the chance of an accident in the from the get go. The more positive reinforcement you get under your belt before you have to deliver a negative the better. You are going to go back to treating your dog for going outside, it is a huge deal if they go outside, that is one less stain on the carpet. Make sure that they get the treat as soon as they are done, don't wait to come in the house to treat them. You go out and wait until they finish.
With all of this supervision you will see if they are going to go in the house; when they do let natural reaction lead the way. We naturally yell NOOOOOOOOOOO when we see a dog peeing or pooping on the floor, keep it short and intense. You deliver the message and then stop, calmly take the dog outside and wait for them to finish out there. No grudges, no prolong nagging, an initial AHHHH and that's it. You do not want to scare your dog but you do want get your message across, it is not acceptable to go to the bathroom in the house. With many repetitive treat deliveries for going outside the house training will be well under way. But you must keep it up, do not think you are out of the woods too soon. Best to keep treating for going outside, it's much preferable over cleaning the carpet, no?
If you fail in supervising and your dog goes in the house; smack yourself in the head, you failed. Calmly put your dog outside and clean up the mess. Every time you don't supervise, you miss your chance to educate, you failed not your dog.