l was searching for a chip for my Infiniti G35 coupe, to get a little better MPG and some of them on ebay sound over reality. Some of them say up to 70 MPG. l know thats impossible but is it at least doing any improvement ?

No man, that stuff doesnt work. unless it costs around $150.00 from a known performance company than it will work. Those expensive ones usually give like 20-30 hp and they actually do reduce gas mileage but not significantly. The chips that are like $10 are just resistor chips that do not do anything at all. l know this from experience.
Dodge Charger SRT-8.. 430 hp

no they dont..i know exacly what your talking about..i thought about them at first too.

i ended up getting the UniChip..it was around 900bucks, but now l can control the fuel/air ratio, more hp or torque..its fun..