Why is is so hard to find advertisement marketing agencies that actually work?

I'm still a fairly small business so I cant afford to try everyone on the market but so far everyone I've tried just kind of sucks at there own job. Now marketing really isn't my forte which is why I'd prefer to just pay someone to do it for me. Here's the problem though.

Everyone wants $500-$1200 start up fee + $500-800 monthly fee. I can afford that just fine when my calendar is full but I'm with my 2nd company already and so far both of them are just trash. The first guy was alright but it always took 3 or 4 days to get responses to my messages. My guy I'm using now I'm just closing in on a month of using him; he has a teem of over 10 employees, he's usually vary responsive, and he always has a lot to say about what he's working on. But in 1 month of using him so far I've gotten 10 leads and 4 of them booked. Now for some business models out there that might be fine but for me I need 2 jobs a day to stay busy.

So I'm just curious what all of you think about this and if y'all have any advice for me here?