  The simplest models of inflation predict small non-gaussianities and a
featureless power spectrum. However, there exist a large number of
well-motivated theoretical scenarios in which large non-gaussianties could be
generated. In general, in these scenarios the primordial power spectrum will
deviate from its standard power law shape. We study, in a model-independent
manner, the constraints from future large scale structure surveys on the local
non-gaussianity parameter $f_{\rm NL}$ when the standard power law assumption
for the primordial power spectrum is relaxed. If the analyses are restricted to
the large scale-dependent bias induced in the linear matter power spectrum by
non-gaussianites, the errors on the $f_{\rm NL}$ parameter could be increased
by $60\%$ when exploiting data from the future DESI survey, if dealing with
only one possible dark matter tracer. In the same context, a nontrivial bias
$|\delta f_{\rm NL}| \sim 2.5$ could be induced if future data are fitted to
the wrong primordial power spectrum. Combining all the possible DESI objects
slightly ameliorates the problem, as the forecasted errors on $f_{\rm NL}$
would be degraded by $40\%$ when relaxing the assumptions concerning the
primordial power spectrum shape. Also the shift on the non-gaussianity
parameter is reduced in this case, $|\delta f_{\rm NL}| \sim 1.6$. The addition
of Cosmic Microwave Background priors ensure robust future $f_{\rm NL}$ bounds,
as the forecasted errors obtained including these measurements are almost
independent on the primordial power spectrum features, and $|\delta f_{\rm NL}|
\sim 0.2$, close to the standard single-field slow-roll paradigm prediction.
