Both are introverted thinkers from central quadras.
I've seen people having trouble telling them apart. Some fictional characters in particular seem to be alternatively typed ILI-Te or LSI-Ti.
Their taste for manual labor is quite a poor way to tell the difference. A LSI from a rich family knows he has to distance himself from such endeavors if he wants to attain a good position. An ILI from a poor family is most likely to have helped his parents with practical hand work, and will be less likely to know that it is better to distance yourself from manual work.
I have known two LSI-Ti I believe (I am their beneficiary). They seemed to have much more self-control than I had. My ideas command me, I am wavering. They hold themselves with much more dignity. They pause, they think, only then they will tell their perfectly articulate answer.
It is better to not show any hint of betrayal with them. Once, I've made the mistake of telling one of them that "I might relocate in another district" (as a consequence we wouldn't see each other anymore). It was mostly to see her reaction. Well, from this time, she saw me very differently (as a traitor in every domain basically). Even though we weren't really close beforehand.
However, I have to say I found them to be very boring. They seemed to have a tendency to state very obvious things and to be impressed by the creativity of very banal works.
How do you make the difference between both ?