a friends has no problems selling to the ones ive tried to use just seems to be me atm, trying to sell plat to the morphus carriers.
Well, again, it depends on the carrier. They are all player owned, so they don't have all the same amenities.
When you buy a carrier it doesn't come with anything, really. You have to buy modules so you can repair, equip, refuel, have a market, etc. Plus you have to have them all turned on to work and a lot of guys shut them down unless they themselves are using them to save money on the monthly upkeep. You could be just having bad luck.
I tend to never try to sell anything to a carrier. I use bases only because the carriers are so unpredictable in what they may or may not have available. I use them for emergencies only to refuel or repair and that's it.