Confirmed: PageRank weighs a link by the importance of the page casting it, so one link from a respected site outweighs dozens from obscure ones. Google publishes no domain "trust" score (Authority and TrustRank). Unconfirmed: that referring-domain counts cause rankings (vendor studies show only correlation), that .edu, .gov or country-code domains pass a bonus, and that old domains or old links pass more. The advice to get links from different "Class C" IP blocks dates from link networks hosted on one server; classful addressing ended with CIDR in 1993, Google documents no IP-based link grouping, and most sites now share CDN addresses.