We've all heard it, most of us have said it. "That sounds expensive."
This may be a bit tricky for many of us. As an artist myself, I've seen lots of others' work. Sometimes my first thought looking at a piece is 'wow, that's a lot', other times it's 'wow, that's really under priced'.
It doesn't have to mean the work is poor, or that you don't like it. Whether or not you like the artist's work is very subjective. Regardless, hopefully the artist has a good idea of how long their works take to make, what similar works are selling for, their experience and training, and what they need or want to make per hour. Maybe they even charge accordingly.
Sometimes, they may give you a discount - for example if you're a friend or repeat buyer. If you see a piece you really love, but you can't afford it, that doesn't (necessarily) mean it's over priced. Instead of asking for a steep discount, which will only make the artist feel like you don't really value their work, try asking them to create a similar piece (just don't expect an exact copy!) custom made for you in a smaller size. Alternately, ask them about a print of the original piece. Another option is to ask if you can pay in instalments. That way, the artist gets paid for the piece, and you get the art you love and can space out the cost over a set amount of time, making it easier for you to afford.