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Adding to what normalised says
The telescope you have probably has a focal length around 1.5 metres and the eyepieces I guess are 26mm and 9mm. Probably a cheaper brand.
The 26 mm eyepiece will give a field of view around 1 degree and the 9 mm around 25 arc minutes. These cheaper eyepieces tend to have much poorer focus as you view objects off the centre of the eyepiece.
The 26 mm eyepiece will give the most pleasant view of most sky objects because you will get more light into a smaller area. The 9mm is best for planetary viewing.
The 30mm your friend uses will give an even wider field of view than the 26mm and it obviously is of much better quality and probably has a much better focus across the viewed area.
Most telescopes of the type you have will give much better views when correctly collimated and used with high quality eyepieces. Spending surplus money on a the best 30 mm eyepiece you can afford is still the cheapest method of improving performance.
Until you understand more about eyepieces and how to check them I would advise against a S/H eyepiece that could be a bomb. Too many people have been caught before paying good money for this type of object that can often be bought cheaper from a registered dealer.
Barry
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