We originally met Sath when he picked us up from the airport. He was friendly, engaging and keen, so when we wanted a trip to visit the kulan mountains and bang mealea temple we figured cut out the middle man! A bit of negotiation via WhatsApp later and he sorted us kulan park entry tickets and transport at less than we would have had to pay via the hotel with less hassle and a later start as he picked up the tickets for us in advance.
While he's not an official tour guide (yet!) he was very helpful in timing our visit so we had more chance to take photos without the hoards in the way, which is our thing, and making sure we got to see all the hiden gems of kulen. I'm sure he'd put similar thought into accomodating your thing whatever that happens to be.
One thing to note with Seam Reap in general is that the local banks have started not to honour the full face value for dollars which are ripped/damaged in some way in recent months. As a result, make sure that you have either Cambodian Riel or very crisp greenbacks, or you will be asking the locals to accept an extra 10 to 15% discount at the point of payment, which can be stressfull all around, because unlike the major tourist venues and hotels, most of the locals, including Sath, can't take a card yet.