Before you skip this because you don't like the limited custom field offering in Gmail's Contacts application, I'll show you a way to get those buyer and seller information items into a system that's easier to maintain and more "on-demand" oriented. If you become a Gmail user, you can manage your prospects and contacts information inside Gmail quite efficiently. Remember that this series is about free or very low cost real estate business management solutions. And Gmail is a big piece of this whole office solution.
You may not have similar needs, but think about how you communicate with prospects, business contacts and transaction participants. I do it mostly with email, as I like that written record better than a "he said-she-said" recollection of a phone call later. If there is texting involved, I can have them forwarded as an email, as well as send out of email, to get them into an email system for storage as well. So, I found that almost all of my daily business and communications were ending up in email. Since I use Google Voice and have voicemail transcribed and sent to my email as well, there's not much that doesn't end up in my Gmail account.
Since the Gmail Contacts application is very efficient at the basics of Names, Addresses, Emails, Birthdays, etc., that takes care of the vast majority of my CRM daily activity. The only thing missing is a set of custom fields for buyer and seller preferences and real estate related information. Well, I found a way to work that out as well, and have everything in Gmail. No, I didn't find a way to add a bunch of custom fields to Contacts, but I did find a way to get them into Gmail in an efficient way that allows easy look-up later. Here's a link to instructions and a set of email fields you can copy if you want.
That article will take you through how I have all of my contact/prospect information and special real estate information items in Gmail. Then it shows you how easy it is to access every bit of information about a contact, as well as every communication you've had with them. Considering the fact that emails with attachments are there as well, documents will be available with a click, without extra effort to upload them to another contact manager.
If you're also doing snail mail for marketing, it shouldn't keep you from adopting these methods. Keep another mailing list database, or if you use a vendor, just email them an export out of Gmail before new mailings. Keeping your Gmail Contacts up to date will allow you to export a fast .csv file of mailing addresses for that purpose. Since fewer of us are doing snail mail on a regular basis, it's a small trade-off for a free and fast CRM data system.