no support, people should have there own decision if they want to apply them by teamviewer or if the person wants it applied by teamviewer. it is just recommended so you don't get blown off if it does not work
That's ridiculous; trades can be done however the hell traders want to do them. The compulsory use of MM's would reduce scams as well, but obviously they're not required either.
If you feel more comfortable using Teamviewer, do so. If a particular seller only wishes to sell using Teamviewer, they can state that in their terms of sale also. But it's up to each trader to decide what they feel comfortable with.