By representative do you mean Account Manager to create and look after your campaigns? It depends on what you require. You may run a online store that needs 100 products promoted or an image host or a forum or a blog, each are different + your may want different things and have a big daily spend or a small daily spend.
I come to know u need to spend more than 500 Usd so that Google allots a representative... Sorry if i am wrong
if that's what he's talking about I don't think it's $500 usd, I manage accounts where people spend over $500/week and they don't have an account representative.
You might be able to beg for one once you start spending 10k per month consecutively, but reps are usually only handed out to account that have 50k a month spends or higher. If you are under this mark, you can get a rep by being associated with an agency who has some pull
I got an account manager spending a small amount per day. I think they consider the account performance(CTR, cost per click) as a criteria.
Is he a dedicated account rep or a general rep? Will he do whatever you want or just answer simple technical questions.