He's not trying to scam someone in the normal sense. July 9th is when the Byteball airdrop will happen, and Bitcoin holders will get free Byteball based on the amount of BTC they hold. Byteball is worth a decent amount right now, and OP is almost definitely trying to "buy" byteball from you via signed message and than instantly selling for profit.
Each 1 BTC you hold gives 0.0625 GB, and 1 GB is trading at over 0.3BTC right now.
Didnt know people would ask for a low amount for byteball but he shouldnt have phrased the sentence that way then.