A lot of the transport info would depend on ambient temps etc. I'd normally be thinking of a cooler with reptile heat packs - but that is entirely because I am in a cold country in the middle of winter. If you are in a heated car then you would need to re-think that whole approach to avoid overheating them.
Haggling is ok I think but try not to be too aggressive and end up low-balling.
I'd also ask how the food was prepared and offered just to try and keep to a similar approach until the animal is settled. It's more of a must ask for F/T than live obviously but there may be things the seller does you hadn't thought of.