very open and large question
1)you have USA brands sold on ebay
2)YOu have a ton of China brands sold on ebay from
CMP , Willshobby , Flymodels , flyboy models , just too many to comment on unless you can show the brand

General rule for me is "benifit to risk ratio " I am a builder , so example , If i can get a nice Warbird in the 70" span range for $150 or less , then its totally worth it for me to bash it and start a rebuild .

If you dont like to tweek , bash or even reinforce your arf from Ebay , dont buy them , you will only risk your investment and the safty of you and people around you .
Most arfs need work and no-name imports may need twice the work , again it depends on the brand .
My Willshobby Seafury was purchased for $149 , worth every penny , same with my $99 Balsa Products 65" P40 , and my 70" Flymodels Hellcat ($129) .
I also got a 70" Jettect P47 for $129 and a FW190 71" from Jet Tech for $189 , all will undergo bashes to more scale but for me its worth basement hunting and they fly well (at leaste the ones I have built )