I'm MUCH more likely to look at a postcard than an unsealed letter.

When Wholesaling, you would want your team to focus on marketing (yellow letters, post cards, etc), negotiation/acquisition, and another person to focus on building a buyer's list to unload the wholesale properties.

Be the one that keeps mailing longer than others do.And something I may start...and you might want to try, spread your letters out farther with a post card in between, that IS the same every time.  

It's 17.5 cents postage per postcard (over-sized postcards...

If you're doing a postcard, it probably doesn't matter. 

From what I've read the typical response rate is 1% to 10% depending on what type of piece you're mailing (post card, zip letter, typed letter, handwritten...)

@Michael Quarles has a great site where you can choose which one you like best---and he has some super choices. if you go to his profile here on BP you will see the link.He also sells lists ;-) I love OOS (out of state) owners and free&clear lists.Some people use the same postcard every time; others will use the same one for 4 consecutive mailings---over a period of 4-6 months and then switch.

I have tried oversized and undersized postcards in split tests, and they just dont convert as well. 

If you want to check out samples of postcards I have sent out I uploaded a couple in the BP fileplace.Frank

If my first mail piece was a yellow letter and now I'm sending a postcard, do I change all the numbers-- and now need 18 numbers-- or do I keep one number throughout the whole campaign?