The best strategy I've found to securing a deal is to go right away. Keeping an eye on the used market and knowing the buy/sell price for a lot of things will tell you when something is a great deal, and that if you make contact with the seller to let them know you are on the way. Now, that's not always possible, but from my experience on the selling side, you can sort out the flakers, and those serious pretty quickly. And there are a LOT of flakers. One of the reasons I HATE selling stuff. Facebook market place has made it much better, but kijiji is terrible for that. Too much anonymity. With facebook people are a bit hesitant to be idiots and waste your time when their name and entire breakfast history and dog pictures are on the line lol. Still doesn't stop some though. Be assertive and if it's a good deal, take a risk. Commit to it, send a deposit if needed and sort the details out afterwards. Fortune favours the brave.
With a mill like that he probably had at least 20 or more emails about it. It's not always about first come first served, and sometimes tough to keep track of, although I tend to lean that way (even being burned by no shows before), sometimes it's the path of least resistance that gets the gold. If a guy says he can come right away with cash and a trailer he goes first in line. There's always going to be 5 guys that will show up Saturday morning, and maybe 1 might actually show. Sometimes you risk losing a serious buyer that was 2nd in line for a flaker that might show up a week later and try to haggle you down a few hundred bucks. It's tough as a seller to read minds and intent through emails. A bird in hand....
While that mill was a decent deal, I'll still think you can find a better value (maybe not as cheap) for something with a DRO, powerfeed and some tooling if you are patient and are able to pounce. Use this time to find a source for a trailer to borrow/rent on short notice. Come up with a moving strategy, and maybe pick up an engine hoist, cribbing, rollers, etc so that when the time comes you can say "I'll be there in 2 hours, I'm leaving right now". I can almost guarantee success that way.
Your needs might be different but I consider a DRO and powerfeed essential on a knee mill. I wouldn't even consider buying one without those unless it was much cheaper than that one. As I'd rather not go through the time and expense of installing them. Some enjoy cranking handles and counting revolutions. I don't, I enjoy making stuff the quickest most efficient way possible.