Offers - how to get faster, more accurate...?

Finally made an offer; was refused (wasn't seen as a "serious" offer because it was so low); am now wondering where realtors get comps (and where I can get what she gets) cuz hers and mine were so different - and she had so many more properties show up in hers!

Also wondering how one spots the good deals on paper or on sight and then gets comps and an offer prepared and presented - FAST! For the last four weeks, it seems as soon as I find it, drive by (to check out neighborhood, get a glimpse of what might be needed in repairs, etc.), find comps, compute offer - it's already pending! This is driving me crazy! The ones that are pending are the ones I was pursuing, so I must be doing something right - but where is it going wrong!?

Am considering making another offer (if the place is still active), but learned there's another way to prepare an offer for holds than for flips - but I don't know what that is (it's just not what I know)! Been reading about CAP Rates, so getting more education, even tho not sure how to apply it.