I never think
of E-bay as a source of components. I am quite sure that
most E-bay sellers are honest, but since components are something I can't
repair and are thus worthless if faulty, I prefer to deal with a
well-known company.
It's fine, actually. Don't buy random piles of unpackaged parts,
I'm sure it is. Most e-bay sellers [1] seem to be totally honest, and if
they claim to be shipping new ICs in the manufacturers tubes (say), I am
sure that's what you'll get.
On the other hand, you get the odd defective part from even well-knwon
distributors. Again, I am sure most E-bay sellers will refund/replace
under such circumstances, but it could be a hassle. It's probably totally
irrational, but I will stick to the likes of Farnell, Digikey, RS
components, etc.
However, to get back to the original question, if a component is not
listed on E-bay but is available from a reputable distributor, I'd not
try to find a substitute for it. And actually, in my case, if I needed a
part that I couldn't find from a distributor and it was listed on E-bay,
I'd probably buy the latter.
-tony