Here are two BR pullets at 12 weeks old. Note the small combs and dark color. Some pullets will be lighter on occasion, however, I have yet to see a humongous comb like yours have on a 9 week old pullet, so all signs say cockerel.
Here is my current BR pullet, Barbara. She is almost 12 weeks old.
roos I have 2 that look just like that but if you are still not sure and you wanna be 100% sure rule of thumb on breeds you have no idea about is wait till it crows or lays an egg then you will be 100% sure without any doubt.
But I know they are roos with bars they are more black if female more whit/silverish if male sorry.
Now, some do not get the hackle and saddles until after the age these boys are. Mine don't have those at nine weeks old usually. I hope I'm wrong, that they are extra light pullets with early combs, but in a couple weeks, you'll be sure.
here is my flock rooster, Dutch, at about 8-9 weeks old. See? No saddles yet.
I'm sure they are roo's...I have three that look identical to them. I have two hens and they look much different than the roos....much darker and no red on the head at all...
Don't know about being an expert, really. I've been wrong a couple times when there were off traits, but it's rare that I miss. This breed is quite easy to sex in 90% of the cases. Lexie and her son Zane were in that 10%. Gosh, one of my hen's daughters produced a very dark cockerel that really messed with our minds, LOL. That was lockedhearts' RuPaul. We went back and forth on him for months on end.