Has anybody bought a used boat through a private seller in Arkansas?
How shall I need to be prepared paper work wise.
What do I need to get from the seller? They don't have boat or motor titles.

Arkansas does title trailers so there should be one of those. For the boat and motor, there should be an MSO. That is a Manufacturer Statement of Origin, basically a birth certificate for the boat, and motor. Each one built has one that goes along with the boat from manufacturer to dealer. If they were not turned in for titles, they should still be someplace.
Without ownership doc's you don't know if there is an existing lien and neither will your state. You will also need a signed bill of sale between you and the seller.
Best thing to do is call Parks and Wildlife and explain what you do have available and what they will need. They might be able to do a title search to be sure there is not a lien in place. If there are no ownership papers of any kind, that does present a problem for you.
Let us know how we can help.
Thank you,
Ken

Go to TPWD website and research...all needed info is there! Can also print off the forms you will need!

I just bought a used boat in Tennessee and did all of the registration paperwork in Texas about a week ago. Forms PW 143 and 144 needed to be filled out and both are signed by the seller. I bought mine in Tennessee where they don't title boats or trailers so they (Texas) wanted the registration card. I took the original title but they didn't really need it but if they title them in Arkansas take it with you. Again, registration card is what they wanted since they don't title them in Tennessee. Make sure the motor and the boat price are listed separately. You need a separate bill of sale for the trailer with the trailer price separated and you'll do the trailer at your local tax office. You'll also need two other forms, one for the boat and one for the motor. I forgot the form name but it's where you transcribe the serial number from the boat or motor or you can take a photo of each serial number also. The form has an area where you take a pencil and put over the serial number and fill in.

The big things from the seller are the bill of sales with price for boat, motor, and trailer listed separately. I used one bill of sale for boat and motor but price broken down then a separate bill of sale for the trailer with its own price. Trailer bill of sale definitely needs to be separated. Seller needs to sign forms 143 and 144, that's very important. Take the titles, registration, forms 143 and 144, and the two forms verifying the serial numbers of the boat and motor. If I find the form number for the serial numbers I'll post it but it's a very simple form. Just found it, It's PWD 504, Verification of Vessel or Outboard Motor Serial Number (PWD 504)

If you want an extra registration card you'll have to ask for it and I think it's around $11. I got one to keep in the boat and one for my wallet.

When in doubt, I call the Garland TPWD. They will tell you exactly what you need for the boat and motor, from any state. I haven't found a good source for that with the DMV but your local office can probably tell you what is needed.