By Deepa Seetharaman SAN FRANCISCO (Reuters) – Amazon.com Inc’s message to investors has always been clear: trust in founder and CEO Jeff Bezos. Some on Wall Street wonder if Amazon may have bitten off more than it can chew. After an unusually busy first half of the year that saw the online retailer spend on developing everything from mobile phones and Hollywood-style production to grocery deliveries, investors are ready to see it curtail its ambitions and start delivering sustainable profits. “It does get frustrating when they continue to spend quarter after quarter and they don’t let the revenue flow through,” said Michael Scanlon, who manages $3.5 billion at Manulife Asset Management and holds shares of Amazon.