@DeathByWalkies I was told all of that too. It doesn't really apply to mine, who never ever gets rewarded in any way for jumping up at people. I cracked that one when out walking him as well as at home. He doesn't jump up at people for attention any more.
What it is with him is the total overload of people in his house. The absolute need to have them, taste them, hug them, assimilate them, make them belong, part of 'us'. His self control disappears. You can see him trying hard to calm down and failing. Trying and failing.
As one great trainer/behaviourist recognised, it's more part of his lack of confidence than a desire for attention. With strangers in the house he loses his confidence, his relaxed certainty that he is safe. So he goes a bit overboard to reassure himself that the strangers are safe, can be accepted.
If visitors can put up with him long enough for him to sniff them, lean on them, lick them a bit, he can assign them their space in the house and forget them. They lose their danger.
Once we recognised his behaviour wan't naughty or attenton seeking it became much easier to help him regain his self control, when to praise and treat him to reinforce it.