This is certainly a scam. If they just wanted to be sure users are holding a good amount of TON on wallet, they could have always checked the balance of the connected wallet. If they wanted transaction activity, they could have just asked for 0.01 TON. A specific and large amount like 0.5 TON might turn into a scam as even though they distribute tokens, its value might not be over the value of 0.5 TON. Even if users makes profit for the talked project, such trend would surely make more and more scams.
with the case of DOGS airdrop as far as I can remember they only require to make some TON transaction regardless of the value, the other project that requires big amount of TON on the other hand are obvious grifter, the altcoin market never ran out of scammer, the 0.5 TON requirement is completely unnecessary, that amount definitely not just magically pop out in their app but have been thought thoroughly by the project maker to make profit from the participants. a good reminder that not all project in the TON ecosystem are safe and people need to look after themselves.
What about a scenario where a project after requesting for such payment from participants actually airdropped but to just about 15% of their participants out of a 100% that made that TON payment task. Can that still be regarded as some form of scam? since the notion has been that most of these airdrops that request some fee to be paid don't usually fulfill their promise.
Yes, I will still regard them as scam because if they received TON from 80% of participants, then they should distribute to all those people that paid that fee. If they would only pay to 15%, when then did they accept fee from everyone? They need to return their ton back if they will not give them any reward.
requiring payment without guarantee that they will give out something is a scam, there are other thing that are similar to this called pre-sale but the thing is, presale guarantee token allocation for anyone who bought the token, but requiring payment without giving something in return but empty promise, is pretty much a scam. I wish people can see through this fat lie, but I know some people are so blinded with the prospect of receiving dreamy returns.