An engine modifier modifies the engine. From there its broken in by the user. If anything the problems had were either a engine problem instilled from the manufacturer or the end user.
I highly doubt anyone goes out there to mod motors with ripping people off in mind. Just doesnt make sense.
Another thing to remember is engine manufacturers dont normally offer warranties with there engines for this statement.
"Due to the nature of nitro racing" These motors dont come with a warranty. What that means is , anyone with half a brain can blow up a motor on command. So lets say your motor has who knows how much fuel through it and you want a new one...you just blow the motor , complain to your engine company or modified and hope to get a new one.
With this kinda things that can go wrong. Its hard for a engine modder to say ok ill take it back and give you a brand new one. In which they have to pay for , then put labor into again...
Buying a modified motor is more of a risk due to investment , nothing more. Its scary buying any 300+ dollar motor , modified or stock. It just means if something goes wrong you have to spend that to get what you had back.
Albeit though most modifiers normally will take a look and assess the situation. But you really cant get mad at them for a blown motor. Most cases it was out of there hands and not there doing.
Every motor is different and engine modders cant forsee the future or use xray vision to see little stress cracks or small things that might make or break a motor.
This is where you might want to invest money into getting the few engine modifiers to break in your motor too. So anything that goes wrong , the engine modifier can bring up to their supplier and of course youll get a motor that makes it.
Otherwise getting a modded engine is probably a safer bet cause they see all these motors all the time and if one doesnt look right , they probably wont even modify or sell it. For two reasons.
1. They dont want a bad rep and
2. They dont want motors sent back, hassle of returns , inspecting, speaking with a disgruntled customer...etc etc.
Best bet is to find an engine modifier for two resasons. Reputation and or price. That way you at least have something to benefit. Either by not paying much either way or at least knowing who did the job knows what there doing and really lays down power.
Im pretty sure most people here know quite a few good engine modifiers. In fact quite a few of them reside on rctech. I wont say names , but any smart fellow can tell you whos good. In fact some of them might of already posted in this thread.