£5 sounds like she wants a 'commitment' (like if you pay then it's not an impulse buy IYSWIM) but not 'making' money on them.
You'll have to let her know if you want boys or girls and get them double-double checked.
I've had both- I'd say if you haven't had guineas before then girls might be easier. They don't need as much room, and you don't get so much of the arsey teenage nonsense that you get with 2 boars when they grow up.
(That's not to say two sows won't have the odd spat though
)
They are lovely babies, very active, bit skitty, nails like razors blades and they run down your sleeve !
It's nice to see their personalities develop. There will be one who is a bit braver, bossier, more forward. But I have never met a nasty guinea (though one of mine when I was a teen was very independant and non cuddly. But she would follow us round like a little dog).
You'll find out what they like to eat (they are very bribeable) and there are lods of threads on 'SuperFurryAnimals' about what is safe/unsafe.What bedding to avoid.
The noises they make is one of the nicest things about them (they are like squeaky Tribbles )
And they don't smell if you keep them clean, unless you get one like my little black Abbysynian boy who has horrible wind. (he's one of a kind though) 
My resident hogs (well, they belong to my DC. My DD is surgically attatched to her boar. My DS is a bit meh so the smaller guinea is mine really) are 2 brothers.
They are lovely, friendly, messy , little critters. Some people say boars are friendlier than sows. No idea, depends on the pigs really.