Transit and radial velocity models were applied to archival data in order to examine exoplanet properties, in particular for the recently discovered super-Earth GJ357b. There is however considerable variation in estimated model parameters across the literature, and especially their uncertainty estimates. This applies even for relatively uncomplicated systems and basic parameters. Some published accuracy values thus appear highly over-optimistic. We present our reanalyses with these variations in mind and specify parameters with appropriate confidence intervals for the exoplanets Kepler-1b, -2b, -8b, -12b, -13b, -14b, -15b, -40b and -77b and 51 Peg. More sophisticated models in WinFitter (WF), EXOFAST and DACE were applied, leading to mean planet densities for Kepler-12b, -14b, -15b and -40b as: 0.11 +/- 0.01, 4.04 +/- 0.58, 0.43 +/- 0.05 and 1.19-0.36+0.31 g per cc respectively. We confirm a rocky mean density for the Earth-like GJ357b, although we urge caution about the modelling given the low S/N data. We cannot confidently specify parameters for the other two proposed planets in this system.