No there is no rule against that. Issue is that more items are generated quick enough to make that a pretty bad business.
Not saying you're wrong, but is that official?
I remember some time in the past, in the runescape section, people made it seem like it was against the jsp rules to basically resell gp. Like you weren't allowed to have 1 thread buying gp at 30fg/1m and have another selling at 35fg/1m. Was that just some unofficial rule, to your knowledge?
Obviously it's not stated in on the rule page but I always remembered it seeming like it was a real rule somehow.