He was in a huge hurry when unexpectedly meeting Tintin and Haddock at the start of the adventure. He practically did not want to speak with them at all. Why did he say a different hotel to them?
Was he trying to deliberately mislead them as he was there doing shady deals with Dawson and hence did not want any extra attention?
Was he in a hurry and simply said the wrong hotel?

He seems to be very hot and cold with Tintin and has a real unpredictable nature in the adventures they share, sometimes he has great respect for him other times he simply wants to kill him!!
As an acquaintance in real life you would really not know how to handle him at all!

Well, in my opinion Tintin has a lot of strange companions. His closest human friends look much older than him and have violent tempers. Captain Haddock drinks all the time even though he promised Tintin that he wouldn't in Crab with the Golden Claws. Calculus can be very sneaky (like in Picaros) and violent (like in Flight 714). Tintin is also friends with the Emir, who has conflicts with Sheikh Bab El Ehr and knows about the slave trade going on in Red Sea Sharks but doesn't do anything about it.

That is as good an explanation as any. When dealing with a reporter like Tintin who happens to have a high sense of ideals, you don't go around telling the likes of him that you are involved in the purchase of weaponry.

In "Black Gold" I seem to recall Muller attempting suicide because he could not face the Emir's torture chambers and the Emir himself seems to consider the process of putting him through a fair trial as complicated, tedious and a waste of time - just like Alcazar in "Broken Ear"!

Tintin sometimes makes me think of some real-life people who because they get to know a certain person socially and see their charm and good side, turn a blind eye to the sometimes odious crimes that they have committed: for example, I've heard of this woman who is in regular touch with a guy and says how pleasant and charming he is. She has expressed the wish of actually being with him when he is released from prison - where he is serving time for the murder of his girlfriend!

Alcazar probably did not want to attract any actual attention, since he was buying weapons and did not want anyone to know he was plotting another revolution.