I have a line on the above carbine. It is a flattop w the carry handle. It has YHM rails and a Daniel Defense sling plate w/ 2 mags I dont know it it was a 9mm from the ground up or if it was converted. Is this a good price? Do I need to know anything special beyond no bolt holding open, need for converted mags etc? Thx in advance.

That would be a good deal for a FT,the CH and rail goodies are a plus.Be warry of a parts and pieces build up,some are just as good as factory units,some are jam-o-matics. Try to somehow set the sale as conditional upon some type of live fire reliability test if seller can't prove it is a factory unit. If the seller has confidence in the gun this shouldn't be a big problem. Don't expect the owner to let you walk away with the gun without buying it,but something reasonable such as meeting you at a range,you provideing ammo and range fees ect.
Good luck,a 9 that runs well is a blast

I may be mistaken, but a call to RRA should confirm.  RRA has only been making complete 9mm rifles for a very short time (a few months at most, I think).  If it is a complete RRA 9mm rifle, the lower should be marked 9mm.  If the lower is marked RRA .223 or 5.56, it is more than likely a custom/home build.  You can always ask the current owner what he bought, how much assembly went into it and who did the assembly.