I suspect it's difficult to rate Resistors by their physical size, - although as you suspect I believe "you can't Transistorise the Watt" - if the Seller is playing up then return the stuff and write it off to experience. If they were cheap, then bin them!
+ If you have plenty of resistors, I'm surprised you are bulk-buying R's that are only slightly higher-rating....can't you parallel them? (or series, although sometime difficult to mount them).
If you have 1/4W then two in series, in parallel (ie 4x in all) will give you 4x the rating at the same (individual) Res . . you know that....so why spend money? If these are 1/4 W then you have made a 1W resistor..... and I think a multi-R may have a greater instantaneous rating, consult the Mfr data sheets.
- that may clarify what your own bulk-resistors are....and that still depends on the ambient temperature.