About now is usually good. Many people have to plan their expenditure, and that revolves around the end of the month when they get paid.
We find in the last few days of the month and the early days of the new month stuff on eBay does well, and the online shop is very busy. Mondays are always manic as folk shop online at weekends. After say the 15th of a month, it is always a bit quieter, and getting quieter still until people are paid.
Seasonal times it drops off. Now for example, they are buying fireworks. In December they are buying Xmas presents. Late January they have winter utility bills. August school holidays they are in Spain or someplace. If its sunny they are in parks buying ice creams for kids and not shopping online.
A weekend of thunderstorms, at the end of a month, means people stay home and shop online.
There are many e-commerce studies on the subject. We defied most studies the last two years by being manic busy all over Xmas and new year. I didn't quite work out why people were buying Dysons and spares on Boxing Day for example; I put it down to people having time off work and getting away from family stuff they prefer to avoid by doing something constructive.
Of course, some people are unaffected by such things, which accounts for sales during periods that are otherwise quiet. I do find spending patterns online a very interesting subject though. We see the odd day where we think the email crashed sales were so few, and another where Google blessed us and we all work all day. Then we see another that is all French orders, then another where everything seems to be going to Newcastle. Or Wales. Or Cornwall.
How is it seven guys in Wales will buy a brushroll on one day? Then the next day 5 DC16 chargers will sell to Borders, Cumbria, Preston and Blackpool. Then the next day three to France? It can only be Google's changing algorithm.
We have days of low online sales that the phone melts on. Then we are knee deep in people in the shop. Other days, we don't see a soul in the shop but the online shop can be in meltdown. Google is a funny animal.
Its always worth timing eBay stuff to end at a good time for better prices. Although that said, auctions generally don't do so well for us. Fixed price sales are better.