I would start by asking if it is their first dog, if it is then try to explain and instruct on proper dog care.
If it isn't then ask what was their past dogs and what were their results with them. And you can start building up from that. Information is the key.
For example my past dog was a golden lab, smart and clever as any. Learned to pee and poo outside and even how to jump and open the door in 1 day. But golden labs are ranked as #3 for dog smartness. Now I have a Great Dane ranked #32, obviously he took a couple of weeks to learn the trick but we got him to. Now his nickname is 32 LOL!
And every race has their own personality, golden labs are born to serve, they only think of how to make their masters happy and food. GD on the other hand well they behave more like cats, they have a great posture and walk very proud and will rarely obey an order they don't feel like.
Now on the food, my golden lab would it to death if allowed, the GD will eat just what he needs even if the plate is served all day long. Really every dog is different but specially every race is different. Probably they had a Chihuahua before and think everything is the same and want to feed him like his Chihuahua, who knows? I would strongly suggest to inquire the background and build up based on info. and experience.
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