Raising the level at which you can send /tells will likely not result in any change in account hacking. I'm pretty sure folks in the business of gilselling are not necessarily the same folks who hack accounts; to assume so is akin to assuming that someone who sells marijuana is also into human trafficking. And, as folks have pointed out, doing so would not stop RMT tells, only delay them; leveling a DoL job to 50 is very easy to do via botting.

Right now, the blacklist system we have isn't too bad; as was mentioned, it takes only a second to add someone. For those worried about filling up their blacklist and then being helpless - try unblacklisting a few of your early ones. I can virtually guarantee that you will no longer receive /tells from those accounts. They may not be deleted, but they HAVE been banned (which is not the same as a deletion).

I'm not against the notion of setting up a system of /tell filters (such as the friend-only, FC-only, etc system mentioned), but I think it would be kind of sad for people to use it, since it would filter out good-natured and honest /tells along with the gilsellers. It may not come up often, but I don't mind helping out if someone randomly asks me for crafting advice when they see me crafting, for instance, or wants to know where I got a piece of gear from.