Rating percentage: High is good, and I won't buy from anyone below 90. Heck, I haven't bought from anyone below 95%. Rating alone is meaningless, because I got burned on a Dutch auction where the seller had 99%. S/he took us all for a ride at $24.95 x 300.
How long they have been a member: I like at least a year with Ebay, although less with a high rating is acceptable.
Location: Not to promote stereotypes, but I am suspicious of anything from Hong Kong or an Eastern European country name with too many Z's in it. I have purchased from Canada and Australia with good results.
Generally, I look at US people who have been a member for a while, and have a great rating. Number of sales doesn't impress me much, but I ask because here's a dilemma: What do you do with a low rating, but a huge amount of sales? You'd think statistically, you'd get dumbass buyers, and when you have a lot of sales, you have more dumbass buyers. But the ratio should reflect that by staying the same, right?
Suppose you have a US seller who has a rating of 98.5%. But in the last week of 889 sales, they've had 29 negatives and 27 neutrals. Would you buy from them?
What other tips do you have?