I'm even hesitant to give you the web address I'm about to give you, because if you haven't looked for it and found it already before coming to the Bigger Pockets forums to ask strangers for help, you're way, way behind the eight ball.

@Chris StevensonI was so glad I spent that $10,000+ on a real estate guru said no one ever (unless they are a paid sponsor / affiliate).

I would also suggest reviewing credentials...50% of the PM firms in the city are not licensed brokers or agents affiliated with brokers....and most of the agents that claim to manage are focused on residential sales...not a great fit.

I have a discovery call with Revedy in a few days, and I can’t find much about them on the web other than their own website.

I only used their web based dialer once and did not really like it, but I should give it some more time and a couple of more tries.

(It used to be monthly, in-person.)They make money if you buy properties from their affiliates, and can provide additional free, one-on-one guidance via their investment counselors.

@Ali Ahmed I am not affiliated with @Mark Ainley but you may be able to find the list he referenced here on the Straight Up Chicago Investor's Podcast website.

There is another way to see the listing prices history if I can't see it on those webs?

Online Auction Sites - Realauction.com, LLCYes you're right, but it's not the only one, there are other platforms depending of the state and the tax lien type (e.g. redeemable has a specific platform), some county has his own system, finally, the main difficulty is to be updated on all upcoming auctions and retrieve the lists to do the research.There are no other platforms for the counties appearing on the Realauction web site. 

There's a guy who has written a book about it up for sale on Amazon (search "Missouri tax sale") which might have answers to your questions (I have no affiliation with the author).