OK.
I sense quite a bit of obfuscation on what the shayla is
Let's clorify the shayla as follows:
Airlines level of hakpada
A. Airlines that have no weight limit at all
B. Airlines that have a weight limit of "you need to be able to lift it into the overhead bin"
C. Airlines that have a theoretical weight limit, just never ever enforce it
D. Airlines that the usually don't enforce the weight/size limit, unless the checkin agent notices something out of the ordinary
E. Airlines that have a weight limt and enforce it selectively, either on certain flights, or during certain seasons.
F. Airlines that have a weight limit, and usually enforce it, just on certain high pressure routes and/or times, choose to priorities timely service over enforcement
G. Airlines that inspect every carryon at checkin and check overweight/size ones for free.
H. Airlines that inspect every carryon at checkin and charge to check overweight/size ones.
I. Airlines that inspect every carryon at the Gate or just before it at a checkpoint and charge for checking overweight/size.
Evasive actions taken to avoid weigh in - partial list
1. Wearing coats, holding umbrella, holding one sefer
2. Packing heavy stuff in the personal item and rearanging after the carryon is weighed
3. Heavy items in pockets, jacket, coat
4. Wearing abnormal amounts of clothing - multiple shirts, pants, sweaters
5. Placing the carryon close to the checkin desk in the hope that they dont notice/weigh it
6. Taking stuff out of the judged to be overweight bag, hgetting the OK from the checkin agent, and repacking.
7. Leaving some of your stuff with a friend, getting weighed, and repacking.
8. Leaving the entire carryon with friend and when asked to weigh/size the carryon saying "Its with my friend/partner"
9. Leaving the entire carryon with friend and when asked to weigh/size the carryon saying "I don't have one"
10. Passing your suitcase over/around the partition at the checkpoint/gate to avoid having it weighed/sized
Cases A,B,C - Theres no reason to be playing shtick anyway.
Cases H, I (and prob F,G too, and maybe even E) I fail to see why anything should be muttar other than 1,2,3,4,and maybe 5,6. I don't see the difference between 7,8,9,10 and not scanning all your items in a self checkout. The stores should inspect more bags, check better, they're fooling themselves!! What's the difference that one thing being stolen is an item and the other is a charged for service??? (I could see a tzad heter in 7, that if the agent says oh thats ok we dont need to weigh it today, she is authorised to do that)
The shalya is what is mutter in cases D, E, F, (G??).
EDIT: (On further reflection, G might actually be the most chamur category bec you see the hakpada is on using the overhead bins with heavy bags, so you may not even be allowed to do 2 or 3)
Further edit: Realized i left out the "remove items, reweigh, repack" option
Lengthy conversation with a posek (RYB's talmid, I learn Choshen Mishpat topics lehalacha by him).
The first half of the question is gneivas daas. The klal is: if they know that people do this, they are essentially letting you do it and it is muttar. (Example mentioned: wearing extra clothing.) If they know but take steps to stop it, and you are simply one step ahead of them, it is ossur. If they SHOULD know (because everyone does it) and are being naiive, we say ihu deafsid anafshei and it is still muttar. You cannot, however, open your mouth and say something untrue in order to save money. Which of these categories you are dealing with must be accurately judged - a posek can't do it for you.
The second half of the question is a uniquely Rabbi Berkovits take (at least, I never heard the subject discussed lemaaseh anywhere else except from RYBs and his talmidim): limdu leshonam dabru sheker. According to this posek, this is defined as doing something that makes you feel dirty, or putting yourself into a situation that a lie must be expressed on a regular basis. RYBs assurs these. If any of the above acts make you feel uncomfortable, RYBs holds it is a problem even if muttar.
@yfr bachur - see if RYBs himself says something similar.