We already know that Blizzard is tweaking arena rules to make it much tougher to artificially inflate your rating by win trading or buying high ranked teams in Season 4, but it looks like they're starting to take it one step further, by cracking down on people who indulge in it.
Reports are coming in from the official forums and from other spots around the web of people getting bans or suspensions (generally 72 hours in length) and having their Season 3 arena gear stripped. The bans are even permanent in some cases, such as that of Sinther of Stormscale, whose account was permanently banned when his friend used it to do some win-trading, with the win trading given as the specific reason for his banning. You can read many of these stories and reports in this forum thread.
Apparently, some people who simply "bought points" from win traded teams or bought win trading teams are getting banned as well. This has caused some confusion among people. Blizzard poster Ananathes confirmed what other posters said: While Blizzard has not cracked down on buying high level teams in the past, or declared it illegal, they do not support it in any way either -- and certainly, some of the new season 4 rules are specifically designed to make it nearly impossible. Blue poster Reythur recommended that anyone who felt they were banned unjustly should contact Blizzard support.
For my part, I applaud Blizzard for this move. It's going to be tough for me, personally, to get much of the new gear, as my teams generally manage to hang around the 1650 rating area, but I understand that Blizzard is looking to legitimize arenas as a challenging and tough but fair advancement system mostly separate from PvP. Firming up the rules and disciplining people who unfairly grab gear by playing the system is certainly a good place to start. By making sure that people who got Arena gear got it by legitimately fighting to a certain rating level against other legitimate teams, the stigma of "welfare epics" will be gone, and Blizzard can feel free to make arena gear legitimately strong without worry about flooding the game with "easy epics."
What remains to be seen is if people who were "caught up" in the bans by buying win traded teams to gain points will be able to get their accounts back. The whole practice of buying points feels shady on its own. But Blizzard's stance on point trading in the past has been "let the buyer beware," at best, so I have a feeling point buyers may be out of luck.
[Thanks for the tip, Ballistic!]