"A lot of advice says to only accept jobs which are willing to pay the rate you're offering..."
IMHO the rule is good, but you don't have to offer the same rate for each job. If there's a job that benefits you, work out what how much that benefits you and quote the appropriate rate. If there's a job that doesn't benefit you, double your normal rate.
Clients insisting on negotiating the rate is a negative signal. It may be a signal that they don't value your work at the rate you're quoting, and this is often a signal that they won't value your work. It may be a signal that they are under financial pressure (i.e. it's high risk for you). Better clients might ask for a discount but normally will agree if you stick to the quoted rate.
IMHO the rule is good, but you don't have to offer the same rate for each job. If there's a job that benefits you, work out what how much that benefits you and quote the appropriate rate. If there's a job that doesn't benefit you, double your normal rate.
Clients insisting on negotiating the rate is a negative signal. It may be a signal that they don't value your work at the rate you're quoting, and this is often a signal that they won't value your work. It may be a signal that they are under financial pressure (i.e. it's high risk for you). Better clients might ask for a discount but normally will agree if you stick to the quoted rate.