Valve start to track down those who buy and sell via cash?

Recently, i have sold some keys to my buyer.
For those who successfully traded with me. i will request them to commend under my steam profile.
Today, when i login into my account, those buyer who commended under my steam profile has been removed from my friend list.
I try to add them back and ask, they said that they didn't remove me from their friend list.
Maybe Valve trying to stop those who buy and sell via cash, but I am not sure whether it is done by Valve or not.
Anyone encounter the same issue?

uh, that would make no sense.
Why would valve just remove friend wise, also if valve did this, the TF2 economy would crash

I looked at your steam profile and there's a comment about someone buying with cash, and they're on your friends list.

T.O.F_Max Feb 26 @ 7:55am
+rep +rep awesome trader. Trustworthy! Don't worry getting scammed, he will not do it! Just traded real cash with alot of keys with this guy!!!
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Also, Sourcerep would be the first to know, since they do cash trades all the time

Thanks for your info.
I re-add them to confirm whether they have remove me or not.
But this is really weird...

Not weird. Logic answer is they removed you without realizing.
Can easily happen if you change to a weird name.

There's a potato on my lawn
It's armageddon

No its GLaDOS, on potato energy and Armageddon is Portal 3

There's a man with a hat

HE'S GOING TO KILL US ALL

If it makes sense to you, some traders, like myself, do a few dozen trades per day. Having said that, I can not keep fellow traders on my friends list and usually delete them shortly after every trade. Sorry but there just isn't room for everyone. =)