If it helps, I bought two Bosch crank sensors 0 261 210 131 from Autovaux in their December sale last year. I paid £36.53 each incl VAT and postage (£73.06 for two in total to get the 'free over £50 postage' deal). I have previously bought from Autovaux, and the parts have always been genuine GM with the GM holograms, and have, in my opinion been totally genuine, so I decided to try these crank sensors.
They came in Bosch boxes, with Bosch labels and are identical in every respect to another genuine GM c/sensor I have, apart from no GM logo on the sensor head (obviously).
I have previously used Bosch lambda sensors from them and also AutoDoc, and everytime the supplied parts were genuine Bosch, with the correct ident tags as the GM version.
Maybe some have had issues with the parts supplied by AutoVaux or AutoDoc, but I for one, have had no issues with their service or the parts supplied.
As some parts are now drying up from Vauxhall, I would have no hesitation in buying Bosch or GM parts from them if I didnt have any 'in stock', purely based on my experiences.