when somebody mucks is hand you can check the prev. hand history and it will show what he had. How to determine.. oh well. thats explainable, but it varies in different situations. Most of the time you determine somebody's range its based on his play history. You need to have played with him atleast a few hands to know whether he is loose or aggressive. When people are shortstacked they tend to lose hope, so when a shortstacked player goes all-in I put him on a high card and low card, suited or not. For example A 5. Many times it comes out in a different way, which is worse for him and better for me, 8 5off for example. When I see that a player is tight and suddenly he goes aggressive over a hand, I check for the possibilities of flush and straight draw, based on either high cards, like AK, AQ or pocketpairs, OR suited connectors. If he is on the button and flop comes 5 6 7 or something and he is raising I'd suggest he has suited connectors. Many times I dont trust my instincts and bust out of tournaments or cash games.
It varies every time. You just need to have a history with the player to be certain. But usually those that are shortstacked dont wait too long for a big hand, they just throw it away with the first or second hand they get. Doesnt mean that they couldnt have gotten a big hand, for example AK. I make a lot of mistakes in such positions because I put them on a tilt, call their all-ins and Im actually the dog, not him. It just comes with experience . But once you figure it out for yourself it will be easier for you to catch bluffs and stuff. When I spot a TAG on my table, he raises pre-flop but there are 3 5 8 on the table I would never put him on more than a pair. In such situations I become the calling station, because in most of the cases he raises with a high card because he doesnt want to accept that he waited for so long for a hand and missed the flop. As I said, everything comes with experience.