You got a higher rank but you have a red trust which means you cannot be trusted too. 

OP, if you want to vouch then look for a trusted person. Someone that have a green trust or at least someone high rank without a red trust at least unlike the person trying to ask your vouch.

You have to remember that buyers won't probably trust you because you are a newbee. Vouching someone with a negative/red trust cannot help but can only destroy your market and reputation.