No struggles; but used equipment doesn't drop out of the sky into my lap either. Some of the elements in a successful search and purchase, not necessarily in order...
1. Spec out what you need - time consuming; but essential. Don't buy if you are not confident it meets your needs. What size, hp, cab?, etc.
2. Determine your price range.
3. Determine what trade off you are willing to make between hours on the equipment and cost/time to keep it running. Stick with your decision. For me, low hours and good maintenance.
4. Know how you will transport it between jobs - need a new trailer? CDL? Pay a neighbor to pick it up?
5. Determine the brands you prefer and related model(s) - zero in on two or three only. Not a dozen.
6. Search - dealers, Internet, etc. I have not purchased at auction; but might if I knew the owner, his maintenance practices, and therefore trusted what I was getting...and he died or retired and then an auction.
6b. Determine the asking price range of the brands/models you are interested in. I like to graph price vs hours for the machines I find in my search. I note on the graph the unique features of each: cab? New track? Extra buckets? Clean looking machine and operation? Well maintained? Basically, anything that would impact the price on the graph.
6c. Continue the search until you find at least two, and better three, acceptable machines.
7. Look each over - spend a couple of hours checking each out personally. This is not a 10 minute walk around. Spend enough time that you have looked at every nut and bolt 3 times (so to speak).
8. Run each AFTER looking it over - I prefer to demo for a day; but individual sellers may limit you to a couple of hours at their location.
9. If unsure, rent a similar unit for more more time in the seat to confirm this is brand/model is what you want.
10. Make an offer. Expect a response. Negotiate until YOU are satisfied...or WALK OUT.
11. Prepare a Bill of Sale to take with you when you close the deal...see your attorney or if necessary check the Internet. It should include that the seller has the lawful right to sell the machine, there are no outstanding loans on it,....and other things I wouldn't have thought of. From a dealer that is trusted in the community I will read their bill of sale and make additions or changes if I believe they are necessary. This should not be a stumbling block but part of the process. Any issues with the Bill...take a day and talk to your attorney!!!
Likely others will have more to add. My worst experience was a when looking for a tractor. Just what I wanted became available 60 miles away at a dealer, I liked it but I had not done my homework with the price graph and therefore did not know what amount was competitive...the salesman didn't know how to close a deal...I walked out on the deal and later regretted it.