I've also wondered if others who have been doing this longer and more consistently have noticed any drop in response rate in recent months? Don't know if @retipsterseth, @DanielC , @Jarenb or others have any observations or data on that. I think I heard Justin Sliva and his partner mention on a recent podcast that they've noticed response rates being lower than normal lately.
When I first started out in the Spring, I had good results with my first two mail campaigns, which I understand certainly had some degree of luck involved. My first mailer, for instance, only went to something like 75 owners and produced one pretty solid deal, so I totally understand that numbers like that can't be reliably repeated. Second mailer, also in the spring, went to something like 250 owners, I believe, and also produced a nice deal. However, my third mailer that I sent to about 400 recipients in July totally whiffed, with results kinda similar to what @Tyler_Harris described: a few tire kickers that didn't really want to sell and one belligerent realtor threatening to sue me and report me to my state's AG's office for interfering with his contractual relationship with the property owner (who I didn't know had his property listed on the MLS). Side note: I'm not an attorney, but from what I've read online, one can't be liable for interfering with a contractual relationship that one didn't even know existed. I also thought it was funny because my very first land buyer is an attorney with my state's AG's office, and he and I discussed in generalities what I was doing with marketing and he thought it was awesome. :-)
Anyway, in terms of what I changed or kept the same, for all three of those mailings I used mostly tax delinquent data, with mostly new counties or different owners within a previously mailed county added each time, especially on the (unsuccessful) third mailer which was probably 95+% new recipients, so I don't think it's a matter of having gone back to the same well too many times. I guess you'd call all three mailers neutral yellow letters (yellow paper, handwritten font, no blind offers). On my fourth mailer that just went out (so no results to speak of, yet) I switched to a neutral white letter (type written font). On my first two mailers I only had a phone number in the letter, but beginning with the third mailer I kept the phone number and added a website, as well.
So I've been wondering if that's all just in the typical statistical range of what one should normally expect, or if the seller market has slowed down a bit recently, or if I should keep looking for a problem that's causing my early results not to scale up as well.
Lastly, just in case it's helpful for @Tyler_Harris, I've been using a free Google Voice account, so far, with a voicemail greeting that's just under 2 minutes long, and is pretty consistent with the script in one of Seth's blog posts (which I'm sure I could find, if it would be helpful). As described above, I'm still pretty new to this and have only had some limited results, but I feel this phone approach has worked all right for me so far. I can see when someone has called and not left a message, and I've only given this number out on my land mailers, so pretty much all of the calls at this point should be either legitimate responses or an occasional wrong number. When I do have a missed call / no voicemail left, if the person only calls once and won't sit through my greeting I've just assumed they're either a wrong number or not really motivated to sell at a price I'd be willing to pay, anyway. There have been a couple of cases, though, where someone called repeatedly over a period of days or weeks and never left a message. In those cases, I've tried calling them back to see what was going on. One was a non-English-speaking owner that didn't end up turning into a deal, but generally was still worth following up on, I think, as it did lead to an offer and could have hypothetically gone the other way.