Yeah find out who did the porting and then find out what sort of reputation they have. Do NOT buy ported heads where you cannot find this information documented with paperwork. Dude's word for it is not good enough even if they look great.
Regardless, if you do get them take them to a good shop and have them checked out and cleaned up and maybe even get the valves gone over. I bought a used set of Edelbrocks for my 5.0 years back from the Corral with 2,000 miles on them and had great luck with them but I was careful and had them inspected and the valves cleaned up like I said.
2000 Mustang GT Steeda #0048
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.