Percy appeared in front of him, his super speed was no play. "Listen, you wouldn't be embarassed believe me. I mean I may be 301 years old but I can fight and I've never given anyone the honor of having my protection in a blood pact. And it wouldn't be for you, dumby... it'd be for Amelia's sake. And the more enemies the better, I like to fight fast I tend to run out of opponents also even a better reason to do it for Amelia's sake. Don't turn it down hastily, think on it... And it wouldn't be a burden, unless you stink at fighting terribly badly and in that case you better do it for Amelia's sake because you'd need it terribly. Also I'm never a burden, in fact I can show you a trial of my skills, plus most vampires say you must defeat them in battle before doing a blood pact. So... they'd think you won my assistance."
Seriously Percy knew the good points of this pact for Valentine, of course with every pact there's bad things like a possiblity of dying and in which if Percy didn't do all he could to spare Valentine's life in a battle after the pact was made and Valentine died Percy would be cursed with a curse of all curses for not saving his Pact head... But he didn't have to tell that to Valentine, and anyway if it did happen there is always a way to revive Valentine at the cost of Percy. Percy knew all the little details, only told the human side of the story. Most men didn't know about the full other side of the pact, hence why Vampires often wouldn't enter into such a pact without being defeated.