Hi this is what I found for you on the net about guess and think   Guess /gɛs/ Show Spelled Pronunciation [ges] Show IPA –verb (used with object) 1. to arrive at or commit oneself to an opinion about (something) without having sufficient evidence to support the opinion fully: to guess a person's weight. 2. to estimate or conjecture about correctly: to guess what a word means. 3. to think, believe, or suppose: I guess I can get there in time. –verb (used without object) 4. to form an estimate or conjecture (often fol. by at or about): We guessed at the weight of the package. 5. to estimate or conjecture correctly. –noun 6. an opinion that one reaches or to which one commits oneself on the basis of probability alone or in the absence of any evidence whatever. 7. the act of forming such an opinion: to take a guess at someone's weight. —Idiom 8. by guess and by gosh, Northern U.S. using a combination of guesswork and reliance on luck; hit or miss. Also, by guess and by golly. Origin: 1300–50; (v.) ME gessen, perh. < Scand; cf. Sw, Dan, Norw gissa, MLG gissen, MD gessen, ON geta; (n.) ME gesse.

Hello 00Jorge00 :D "Guess" and "think" mean exactly the same thing with the sentence you're using. They are pretty much interchangeable especially when you don't want to make your sentence into a blunt fact. For example: I guess you're in trouble OR I think you're in trouble The two sentences above isn't as factual or as harsh or as scary as "You're in trouble." While the two other sentences could have the possibility that a person may or may not be in trouble.

"I think you're in trouble" and "I guess you're in trouble" or "i guess so" and "i think so", if used this way then they mean pretty much the same thing. you can also add to the group "i suppose.." guess = a deduction, estimate, speculation, supposition think = believe, deem guess is arriving at a conclusion without thingking too much about it or without the proper knowledge