[Q] How bad is the boot loop issue?

So I am looking to purchase a refurb G4 (or Note 4) for T-Mobile as I'm moving away from Verizon and wondering just how bad and the likelyhood of the boot loop issue actually happening on the G4 at this point? Anything I should ask the seller that might indicate the refurb G4 will be less likely to have the boot loop issue occur?

Thanks for any info in advance. Much appreciated.