This has been covered in detail in the past- never buy anything on your doorstep and never buy artwork from cold callers anyway. I have some "expertise" in this area as a family member runs a gallery and framing business and they see a lot of this stuff being brought in to be framed. A lot of the "charcoal/ pencil" drawings offered door to door are commercially printed or photocopied and are of no value whatsoever. The "oil paintings" may be painted, but if so they are effectively mass produced and the "generic painting style" is easily identified; I've seen the same "painted" image repeatedly over the years. Many of the other "painting" are mechainically produced, perhaps with some additional touching up by hand, I can't be sure. If you like this stuff buy it, but don't pay any more than €20-30 for a large picture (say 600x 450mm) and expect to pay about €80 to have this framed, depending on moulding required etc. These "paintings" can be easily purchased in the Far East for a few euro a piece, so remember that what you're buying is effectively an image and not necessarily what most people would consider a "work of art"; one has no value ( visual wallpaper- nothing else) the other has an intrinsic value.
If you want to buy real art you should visit a small gallery or check out the local art exhibitions or the students exhibitions at NCAD; here you'll be guranteed to get something original and you won't have to spend much more than the €110 your Israeli salesman wanted. Otherwise why not buy a limited edition fine art print- these have a commercial value and won't break the bank either.