...I have been using CL since February and have posted some tips in other parts of the forums.
The spammers are most concentrated in Casual Encounters, which is the category for looking for sex. Overseas spammers have set up shop there worldwide and will both respond to and post ads using bots. You really need to pay attention if you're using Casuals and fortunately, the fake ads/replies are easy to spot.
I reccommend looking in the main W4M and posting a M4W ad. As long as you don't come off as desparate or a creep, you stand a good chance of getting a reply pretty quickly.
Also, a bit of advice in general:
Most "LF Pregnant" ads on CL basically say the same thing "I wanna have sex with a horny 7-9 month preggo like NOW. Here's a picture of my dick. It'ss something I've always wanted to do because reasons. Let's meet up and fuck as soon as possible. Yes, this is my dick and it's awesome. Reply back ASAP so we can fuck!"
Try putting a bit of thought into your ad to make it stand out. And no dick pics. They don't like that. Not unless they're really a whore or want to give you an STD. LOL.